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These are the user uploaded subtitles that are being translated: 1 00:00:04,472 --> 00:00:08,640 Narrator: THE FATE OF OUR GALAXY HANGS IN THE BALANCE. 2 00:00:08,642 --> 00:00:14,880 THE MILKY WAY IS DYING, AND WE DON'T KNOW WHY. 3 00:00:14,882 --> 00:00:19,785 OUR GALAXY, LIKE ALL GALAXIES, HAS A LIMITED LIFE-SPAN. 4 00:00:19,787 --> 00:00:23,622 AFTER THAT, IT'S LIGHTS OUT. 5 00:00:23,624 --> 00:00:26,492 Narrator: THE RACE IS ON TO FIND A SMOKING GUN. 6 00:00:28,829 --> 00:00:32,598 IT'S SAFE TO SAY RIGHT NOW THERE ARE MANY WAYS TO KILL A GALAXY. 7 00:00:35,803 --> 00:00:39,738 Narrator: IT'S A COSMIC CRIME SCENE INVESTIGATION. 8 00:00:39,740 --> 00:00:42,908 IS IT MURDER MOST FOUL? 9 00:00:42,910 --> 00:00:45,010 OR IS IT DEATH BY NATURAL CAUSES? 10 00:00:47,314 --> 00:00:49,782 Narrator: THE SUSPECTS ARE LINED UP. 11 00:00:49,784 --> 00:00:52,251 THE INTERROGATION IS UNDERWAY. 12 00:00:56,257 --> 00:00:58,557 IT'S ANOTHER EXAMPLE OF THIS BIG UNIVERSE OF OURS 13 00:00:58,559 --> 00:01:01,093 THROWING PUZZLES AT US THAT NOW WE HAVE TO SOLVE. 14 00:01:04,031 --> 00:01:07,266 Narrator: WHAT IS KILLING THE MILKY WAY? 15 00:01:07,268 --> 00:01:10,269 -- Captions by VITAC -- www.vitac.com 16 00:01:10,271 --> 00:01:13,272 CAPTIONS PAID FOR BY DISCOVERY COMMUNICATIONS 17 00:01:13,274 --> 00:01:23,282 ♪♪ 18 00:01:23,284 --> 00:01:25,517 ♪♪ 19 00:01:25,519 --> 00:01:27,853 EARTH. 20 00:01:27,855 --> 00:01:30,422 OUR HOME. 21 00:01:30,424 --> 00:01:34,626 JUST ONE OF 100 BILLION PLANETS 22 00:01:34,628 --> 00:01:38,897 ORBITING 400 BILLION STARS 23 00:01:38,899 --> 00:01:42,568 THAT MAKE UP AN IMMENSE GALACTIC SPIRAL... 24 00:01:44,572 --> 00:01:47,106 ...THE MILKY WAY. 25 00:01:49,877 --> 00:01:52,478 Thaller: GALAXIES ARE WHERE STARS FORM, 26 00:01:52,480 --> 00:01:54,813 AND, OF COURSE, PLANETS FORM AROUND STARS, 27 00:01:54,815 --> 00:01:56,648 SO THE STORY OF THE EARTH, 28 00:01:56,650 --> 00:01:58,884 OF YOURSELF, OF THE SOLAR SYSTEM 29 00:01:58,886 --> 00:02:02,321 HAS EVERYTHING TO DO WITH THE STORY OF THE GALAXIES. 30 00:02:05,626 --> 00:02:10,863 Narrator: THE STORY OF THE MILKY WAY BEGINS 13.6 BILLION YEARS AGO, 31 00:02:10,865 --> 00:02:13,465 JUST AFTER THE BIG BANG. 32 00:02:13,467 --> 00:02:17,536 IT'S A TIME WHEN THERE ARE NO PLANETS AND NO STARS -- 33 00:02:17,538 --> 00:02:22,741 JUST A VAST, LUMPY SOUP OF SUPERHEATED HYDROGEN GAS. 34 00:02:25,479 --> 00:02:28,647 OVER MILLIONS OF YEARS, THE TEMPERATURE DROPS, 35 00:02:28,649 --> 00:02:33,051 AND GRAVITY COMPRESSES THE LUMPS DOWN, UNTIL EVENTUALLY 36 00:02:33,053 --> 00:02:37,856 THE HYDROGEN MOLECULES FUSE AND IGNITE A STAR. 37 00:02:42,329 --> 00:02:47,833 IN TIME, BILLIONS OF STARS BURST INTO LIFE. 38 00:02:47,835 --> 00:02:51,103 AND THE MILKY WAY BEGINS TO TAKE SHAPE. 39 00:02:51,105 --> 00:02:56,175 ♪♪ 40 00:02:56,177 --> 00:02:58,911 YOU CAN THINK OF A GALAXY AS SORT OF LIKE A HUMAN BEING. 41 00:02:58,913 --> 00:03:01,346 WHEN YOU'RE YOUNG AND IN YOUR ADOLESCENT STAGE, 42 00:03:01,348 --> 00:03:02,814 YOU'RE VIBRANT AND ACTIVE. 43 00:03:02,816 --> 00:03:05,584 THAT'S A YOUNG GALAXY FORMING STARS IN A CRAZY WAY, 44 00:03:05,586 --> 00:03:07,219 AND IT'S NOT EVEN FULLY FORMED YET. 45 00:03:07,221 --> 00:03:09,888 AT A CERTAIN POINT, GALAXY REACHES MIDDLE AGE, 46 00:03:09,890 --> 00:03:12,491 AND A MIDDLE-AGED GALAXY REALLY IS WHAT IT'S GOING TO BE -- 47 00:03:12,493 --> 00:03:13,792 IT HAS ITS SHAPE -- 48 00:03:13,794 --> 00:03:17,062 BUT IN THE LONG RUN, A GALAXY WILL STOP FORMING STARS, 49 00:03:17,064 --> 00:03:20,699 AND EVENTUALLY, JUST LIKE WE ALL DIE, OUR GALAXY WILL DIE. 50 00:03:24,004 --> 00:03:27,806 Narrator: SO, AT WHAT STAGE OF LIFE IS THE MILKY WAY? 51 00:03:27,808 --> 00:03:30,409 IS IT A HEALTHY, ACTIVE YOUNGSTER, 52 00:03:30,411 --> 00:03:32,578 OR IS IT HEADING FOR ITS DEATHBED? 53 00:03:35,783 --> 00:03:39,518 SCIENTISTS CAN DETERMINE EACH GALAXY'S STAGE OF LIFE 54 00:03:39,520 --> 00:03:42,387 BY ITS COLOR. 55 00:03:42,389 --> 00:03:47,226 Sutter: SO, WE SEE DIFFERENT COLORS OF GALAXIES IN THE UNIVERSE. 56 00:03:47,228 --> 00:03:49,761 WE SEE GALAXIES THAT ARE TINTED BLUE 57 00:03:49,763 --> 00:03:54,499 AND GALAXIES THAT ARE TINTED RED. 58 00:03:54,501 --> 00:03:59,705 WHEN WE SEE A BLUE GALAXY, THAT TENDS TO BE A YOUNGER GALAXY 59 00:03:59,707 --> 00:04:04,009 FULL OF BRIGHT, HOT, NEWLY FORMED STARS. 60 00:04:06,480 --> 00:04:08,647 WHEN WE SEE A REDDER GALAXY, 61 00:04:08,649 --> 00:04:11,817 THAT TENDS TO BE A DIMMER, OLDER GALAXY 62 00:04:11,819 --> 00:04:15,654 THAT ISN'T FORMING NEW STARS IN THE PRESENT MOMENT. 63 00:04:15,656 --> 00:04:18,857 ALL ITS STARS ARE AGED AND OLDER AND REDDER, 64 00:04:18,859 --> 00:04:22,494 AND SO THE ENTIRE GALAXY CASTS A DIFFERENT HUE. 65 00:04:22,496 --> 00:04:27,866 ♪♪ 66 00:04:27,868 --> 00:04:32,804 Narrator: SO, WHAT COLOR IS OUR GALAXY? 67 00:04:32,806 --> 00:04:38,777 IT'S A SIMPLE QUESTION, BUT THE ANSWER IS HARD TO COME BY, 68 00:04:38,779 --> 00:04:41,713 EVEN THOUGH WE'VE BEEN LOOKING AT THE MILKY WAY 69 00:04:41,715 --> 00:04:44,783 FOR THOUSANDS OF YEARS. 70 00:04:44,785 --> 00:04:46,852 THE TERM "MILKY WAY" IS ANCIENT. 71 00:04:46,854 --> 00:04:49,054 IT GOES BACK TO A TIME WHEN IN THE DARK SKY, 72 00:04:49,056 --> 00:04:51,290 PEOPLE NOTICED THERE WAS THIS LIGHT BAND 73 00:04:51,292 --> 00:04:53,625 THAT ACTUALLY WENT FROM HORIZON TO HORIZON, 74 00:04:53,627 --> 00:04:54,860 AND THAT BAND TURNED OUT 75 00:04:54,862 --> 00:04:57,095 TO BE MADE OF THOUSANDS AND THOUSANDS OF STARS 76 00:04:57,097 --> 00:04:59,798 ACTUALLY TOO FAR AWAY TO SEE INDIVIDUALLY. 77 00:04:59,800 --> 00:05:01,600 BUT IT TOOK US A LONG TIME TO REALIZE 78 00:05:01,602 --> 00:05:06,538 WHAT THE SHAPE AND THE SCALE OF THE MILKY WAY GALAXY IS. 79 00:05:06,540 --> 00:05:09,408 THE AMAZING THING TO THINK ABOUT IS THAT WE ACTUALLY DON'T KNOW 80 00:05:09,410 --> 00:05:11,710 OUR HOME GALAXY VERY WELL AT ALL. 81 00:05:11,712 --> 00:05:15,414 WE ACTUALLY LIVE IN THE MIDDLE OF THIS DISK OF GAS AND DUST, 82 00:05:15,416 --> 00:05:19,418 AND THAT OBSCURES OUR VIEW OF THE LARGER MILKY WAY. 83 00:05:19,420 --> 00:05:21,987 USING VISIBLE LIGHT, WE CAN'T EVEN SEE TO THE CENTER, 84 00:05:21,989 --> 00:05:26,158 LET ALONE THE OTHER SIDE OF THE MILKY WAY GALAXY. 85 00:05:30,164 --> 00:05:32,764 Narrator: THE SOLUTION IS TO USE A FORM OF LIGHT 86 00:05:32,766 --> 00:05:36,735 THAT PASSES THROUGH THE GAS AND DUST -- 87 00:05:36,737 --> 00:05:38,303 INFRARED. 88 00:05:41,809 --> 00:05:45,677 THIS IS THE SLOAN DIGITAL SKY SURVEY TELESCOPE 89 00:05:45,679 --> 00:05:50,115 AT THE APACHE POINT OBSERVATORY IN NEW MEXICO. 90 00:05:50,117 --> 00:05:53,418 IT'S MAPPING THE GALAXY USING INFRARED 91 00:05:53,420 --> 00:05:57,189 AND GIVING SCIENTISTS UNPRECEDENTED INSIGHTS. 92 00:05:59,793 --> 00:06:02,994 THE FIRST SENSITIVE INFRARED OBSERVATIONS REALLY WEREN'T DONE 93 00:06:02,996 --> 00:06:04,963 TILL THE LAST 15 YEARS, 94 00:06:04,965 --> 00:06:07,265 AND EACH OF THESE NEW WINDOWS ON THE UNIVERSE 95 00:06:07,267 --> 00:06:09,067 TEACH US DIFFERENT THINGS. 96 00:06:09,069 --> 00:06:14,139 ♪♪ 97 00:06:14,141 --> 00:06:15,707 Narrator: IN THE LAST 15 YEARS, 98 00:06:15,709 --> 00:06:21,046 SLOAN HAS SURVEYED MORE THAN 250 MILLION STARS, 99 00:06:21,048 --> 00:06:26,318 ANALYZING THEIR LIGHT TO WORK OUT THE COLOR OF THE MILKY WAY. 100 00:06:26,320 --> 00:06:30,522 AND WHAT SCIENTISTS SAW SHOCKED THEM. 101 00:06:30,524 --> 00:06:32,758 UNTIL VERY RECENTLY, WE THOUGHT THE MILKY WAY 102 00:06:32,760 --> 00:06:34,760 WAS A YOUNG, HEALTHY GALAXY, 103 00:06:34,762 --> 00:06:36,228 BUT NOW THERE'S EVIDENCE 104 00:06:36,230 --> 00:06:39,664 THAT WE MAY BE ENTERING THE PATHWAY TO DEATH. 105 00:06:41,969 --> 00:06:46,505 Narrator: THE SLOAN TELESCOPE REVEALS THAT STAR PRODUCTION IN OUR GALAXY 106 00:06:46,507 --> 00:06:49,508 IS FALLING THROUGH THE FLOOR. 107 00:06:49,510 --> 00:06:52,477 THE MILKY WAY IS DYING. 108 00:06:52,479 --> 00:06:56,148 AND WHEN IT STOPS FORMING NEW STARS, 109 00:06:56,150 --> 00:06:57,716 ITS TIME WILL BE UP. 110 00:07:00,187 --> 00:07:02,754 PARADOXICALLY, OUR GALAXY STILL HAS 111 00:07:02,756 --> 00:07:08,693 STAR-FORMING GAS IN THE TANK, SO IT SHOULD BE HEALTHY, 112 00:07:08,695 --> 00:07:11,196 BUT SOMETHING IS KILLING IT OFF. 113 00:07:15,335 --> 00:07:18,036 SO, THE MILKY WAY GALAXY IS THIS WONDERFUL DISK 114 00:07:18,038 --> 00:07:21,907 FILLED WITH RICH HYDROGEN GAS, LOTS OF DENSE DUST CLOUDS. 115 00:07:21,909 --> 00:07:24,509 IT HAS EVERYTHING YOU NEED THERE FOR STAR FORMATION, 116 00:07:24,511 --> 00:07:27,846 BUT IT SEEMS TO BE SLOWING DOWN AND EVEN TURNING OFF, 117 00:07:27,848 --> 00:07:31,516 AND RIGHT NOW, WE DON'T REALLY UNDERSTAND WHAT THE CULPRIT IS. 118 00:07:36,156 --> 00:07:38,056 Narrator: WITH A GALAXY KILLER AT LARGE, 119 00:07:38,058 --> 00:07:42,260 SCIENTISTS EMBARK UPON THE BIGGEST MURDER INVESTIGATION 120 00:07:42,262 --> 00:07:44,429 IN THE HISTORY OF THE UNIVERSE. 121 00:07:46,400 --> 00:07:48,500 EVERYTHING IN SCIENCE, WHEN YOU'RE EXPLORING A PROBLEM, 122 00:07:48,502 --> 00:07:50,802 IS A BIT LIKE A CRIME SCENE. 123 00:07:50,804 --> 00:07:53,038 YOU'VE GOT THE EVIDENCE LAID OUT IN FRONT OF YOU... 124 00:07:57,177 --> 00:08:00,345 ...AND WE HAVE TO FIGURE OUT WHO DONE IT. 125 00:08:01,548 --> 00:08:10,388 ♪ 126 00:08:10,390 --> 00:08:14,392 Narrator: OUR HOME IN THE UNIVERSE IS DYING -- 127 00:08:14,394 --> 00:08:20,765 NOT THE EARTH, BUT OUR GALAXY, THE MILKY WAY. 128 00:08:20,767 --> 00:08:24,302 IT'S BEEN PRODUCING STARS FOR BILLIONS OF YEARS, 129 00:08:24,304 --> 00:08:26,771 BUT SOON, IT WILL STOP. 130 00:08:28,842 --> 00:08:31,510 OUR OWN SUN FORMED ABOUT 4 1/2 BILLION YEARS AGO 131 00:08:31,512 --> 00:08:32,911 IN THE MILKY WAY GALAXY, 132 00:08:32,913 --> 00:08:36,181 AND WE ARE NOT THE OLDEST STAR BY FAR. 133 00:08:36,183 --> 00:08:38,383 AND YET, TRAGICALLY, WE ACTUALLY SEEM TO BE 134 00:08:38,385 --> 00:08:42,120 ONE OF THE LAST GENERATIONS OF NEW STARS IN THE MILKY WAY. 135 00:08:42,122 --> 00:08:45,557 CURRENT PROJECTIONS SUGGEST THAT IN ABOUT 4 BILLION YEARS, 136 00:08:45,559 --> 00:08:47,559 STAR FORMATION MAY HAVE CEASED ALL TOGETHER, 137 00:08:47,561 --> 00:08:49,427 WHICH IS ALMOST JUST A BLINK OF AN EYE 138 00:08:49,429 --> 00:08:51,329 IN THE LIFE CYCLE OF THE UNIVERSE. 139 00:08:55,702 --> 00:08:59,671 Narrator: TO FIND OUT WHY, SCIENTISTS LAUNCH AN INVESTIGATION. 140 00:08:59,673 --> 00:09:01,973 THE MOST CRUCIAL QUESTION? 141 00:09:01,975 --> 00:09:04,843 HOW IS THE MAY DYING? 142 00:09:06,680 --> 00:09:09,915 TO KILL A GALAXY, YOU HAVE TO GET RID OF THE COLD GAS, 143 00:09:09,917 --> 00:09:12,117 BECAUSE THAT'S WHAT STARS FORM FROM. 144 00:09:12,119 --> 00:09:13,585 THERE ARE MANY WAYS YOU CAN DO THIS. 145 00:09:13,587 --> 00:09:15,687 YOU CAN BLAST IT OUT FROM THE INSIDE. 146 00:09:15,689 --> 00:09:17,889 YOU CAN DRAW IT OUT FROM THE OUTSIDE. 147 00:09:17,891 --> 00:09:20,292 YOU CAN HEAT IT UP SO IT'S NO LONGER COLD. 148 00:09:20,294 --> 00:09:21,793 YOU CAN USE IT ALL UP, 149 00:09:21,795 --> 00:09:23,929 AND THERE'S EVEN MORE WAYS YOU CAN STOP IT. 150 00:09:23,931 --> 00:09:25,497 WHAT WE HAVE TO DO IS FIGURE OUT 151 00:09:25,499 --> 00:09:28,099 WHICH WAY IS HAPPENING IN OUR GALAXY. 152 00:09:30,671 --> 00:09:36,207 Narrator: PERHAPS THE CULPRIT IS INSIDE THE MILKY WAY ITSELF. 153 00:09:36,209 --> 00:09:39,611 A CLUE COMES FROM ANOTHER GALAXY ENTIRELY. 154 00:09:41,648 --> 00:09:48,453 THIS IS W2246-0526. 155 00:09:48,455 --> 00:09:52,457 SCIENTISTS CALL IT A HOT, DUST-OBSCURED GALAXY, 156 00:09:52,459 --> 00:09:54,826 OR "HOT DOG" FOR SHORT. 157 00:09:57,598 --> 00:10:00,699 THIS GALAXY IS 12 1/2 BILLION LIGHT-YEARS AWAY. 158 00:10:00,701 --> 00:10:03,568 IT'S THE MOST LUMINOUS GALAXY WE KNOW OF IN THE UNIVERSE. 159 00:10:03,570 --> 00:10:06,705 IT HAS THE LIGHT OF 300 TRILLION STARS. 160 00:10:10,978 --> 00:10:14,679 Narrator: THE SOURCE OF THE INTENSE LIGHT IS NOT ITS STARS, 161 00:10:14,681 --> 00:10:19,684 BUT A MYSTERIOUS OBJECT AT THE GALAXY'S CENTER. 162 00:10:19,686 --> 00:10:23,188 IT'S A MILLION TIMES SMALLER THAN THE GALAXY ITSELF. 163 00:10:25,926 --> 00:10:29,761 THERE'S ONLY ONE THING THAT SMALL AND THAT POWERFUL... 164 00:10:32,466 --> 00:10:34,699 ...A SUPERMASSIVE BLACK HOLE. 165 00:10:38,538 --> 00:10:41,640 SO, SUPERMASSIVE BLACK HOLES, AS THE NAME SUGGESTS, 166 00:10:41,642 --> 00:10:43,174 ARE INDEED SUPERMASSIVE. 167 00:10:43,176 --> 00:10:47,579 THESE ARE BILLIONS OF TIMES MORE MASSIVE THAN OUR SUN. 168 00:10:47,581 --> 00:10:49,648 THESE ARE GIGANTIC OBJECTS. 169 00:10:52,552 --> 00:10:56,721 Narrator: THE GRAVITY IN THE SUPERMASSIVE BLACK HOLE IS OFF THE CHARTS. 170 00:11:00,260 --> 00:11:02,327 IT SUCKS IN INCREDIBLE AMOUNTS 171 00:11:02,329 --> 00:11:05,664 OF THE HOT DOG'S VITAL STAR-FORMING GAS. 172 00:11:09,703 --> 00:11:12,237 AND AS THE GAS SWIRLS TO FORM A DISK, 173 00:11:12,239 --> 00:11:16,174 THE INTENSE FRICTION SUPERHEATS IT TO MILLIONS OF DEGREES 174 00:11:16,176 --> 00:11:20,945 AND, IN SOME GALAXIES, TRIGGERS HUGE JETS. 175 00:11:20,947 --> 00:11:23,348 WHEN A LOT OF MATERIAL FALLS ONTO THAT BLACK HOLE, 176 00:11:23,350 --> 00:11:25,750 IT CREATES INCREDIBLY ENERGETIC JETS 177 00:11:25,752 --> 00:11:28,653 THAT CAN BE TENS OF THOUSANDS OF LIGHT-YEARS ACROSS. 178 00:11:28,655 --> 00:11:30,722 ALL OF A SUDDEN, YOU HAVE THIS BLOWTORCH 179 00:11:30,724 --> 00:11:33,391 IN THE MIDDLE OF THE GALAXY. 180 00:11:33,393 --> 00:11:35,627 Bullock: BLACK HOLE JETS ARE BAD FOR GALAXIES 181 00:11:35,629 --> 00:11:37,762 BECAUSE THEY CAN SHUT DOWN STAR FORMATION. 182 00:11:37,764 --> 00:11:40,365 THEY CAN HEAT GAS UP, BLOW GAS OUT OF GALAXIES, 183 00:11:40,367 --> 00:11:41,933 AND THEY COULD REALLY KILL THEM. 184 00:11:44,271 --> 00:11:47,839 Narrator: A SUPERMASSIVE BLACK HOLE IS COOKING THE HOT DOG. 185 00:11:51,278 --> 00:11:53,044 WHAT'S GOING ON IN OUR GALAXY? 186 00:11:53,046 --> 00:12:02,487 ♪♪ 187 00:12:02,489 --> 00:12:06,658 IN 2016, SCIENTISTS AT HARVARD DISCOVERED DAMNING EVIDENCE 188 00:12:06,660 --> 00:12:10,095 THAT MAY LINK THE MILKY WAY'S SUPERMASSIVE BLACK HOLE 189 00:12:10,097 --> 00:12:11,863 TO THE GALAXY'S DEMISE. 190 00:12:14,868 --> 00:12:16,334 JUST LIKE THE HOT DOG, 191 00:12:16,336 --> 00:12:20,438 THE MILKY WAY IS SURROUNDED BY A VAST CLOUD OF BLOWN-OUT GAS, 192 00:12:22,576 --> 00:12:27,846 AND THE SCIENTISTS TRACED THE GAS BACK TO ITS SOURCE -- 193 00:12:27,848 --> 00:12:32,784 SAGITTARIUS A-STAR, OUR SUPERMASSIVE BLACK HOLE. 194 00:12:35,789 --> 00:12:37,889 WELL, IT TURNS OUT OUR SUPERMASSIVE BLACK HOLE 195 00:12:37,891 --> 00:12:41,459 HAD A BIT OF A HICCUP ABOUT 6 MILLION YEARS AGO. 196 00:12:41,461 --> 00:12:44,295 THERE'S EVIDENCE THAT SOME MATTER MUST HAVE FALLEN 197 00:12:44,297 --> 00:12:46,798 INTO THAT BLACK HOLE, AND IF IT FELL IN TOO QUICKLY, 198 00:12:46,800 --> 00:12:49,868 IT WOULD HAVE GOTTEN SUPERHEATED BY ITS OWN FRICTION, 199 00:12:49,870 --> 00:12:54,672 AND THIS WOULD HAVE ACTED, IN A SENSE, LIKE AN EXPLOSION. 200 00:12:54,674 --> 00:12:57,008 Oluseyi: AND THAT EVENT WAS HUGE. 201 00:12:57,010 --> 00:13:00,445 OUR GALAXY EXPELLED AN INCREDIBLE AMOUNT OF GAS -- 202 00:13:00,447 --> 00:13:03,882 130 BILLION TIMES THE MASS OF THE SUN. 203 00:13:03,884 --> 00:13:05,750 LARGE AMOUNT OF GAS. 204 00:13:08,688 --> 00:13:10,688 Stern: THIS EVENT MUST HAVE BEEN VERY CATASTROPHIC 205 00:13:10,690 --> 00:13:13,424 FOR THE INNER PARTS OF THE GALAXY. 206 00:13:13,426 --> 00:13:16,161 LUCKILY, EARTH IS IN THE OUTER PARTS OF THE GALAXY, 207 00:13:16,163 --> 00:13:18,563 WHERE WE WERE ABLE TO SURVIVE THIS EVENT. 208 00:13:22,402 --> 00:13:25,370 Narrator: IS THIS THE SMOKING GUN? 209 00:13:25,372 --> 00:13:30,508 IS OUR OWN SUPERMASSIVE BLACK HOLE KILLING THE MILKY WAY? 210 00:13:30,510 --> 00:13:32,777 THE EVIDENCE SEEMS TO MOUNT UP. 211 00:13:35,348 --> 00:13:39,317 BUT SAGITTARIUS A-STAR HAS AN ALIBI. 212 00:13:39,319 --> 00:13:42,520 IT EXPLODED TOO LATE. 213 00:13:42,522 --> 00:13:45,390 SAGITTARIUS A-STAR GOT VERY ACTIVE, 214 00:13:45,392 --> 00:13:47,826 VERY EXPLOSIVE ABOUT 6 MILLION YEARS AGO, 215 00:13:47,828 --> 00:13:50,295 BUT THAT'S SO RECENT, IT SHOULDN'T HAVE REALLY AFFECTED 216 00:13:50,297 --> 00:13:51,729 THE STAR FORMATION RATES. 217 00:13:51,731 --> 00:13:53,097 SOMETHING ELSE IS GOING ON. 218 00:13:53,099 --> 00:13:55,967 THERE MUST BE ANOTHER CULPRIT BESIDES THE BLACK HOLE. 219 00:13:58,171 --> 00:14:02,207 Narrator: STUDIES SUGGEST OUR SUPERMASSIVE BLACK HOLE MUST HAVE BEEN ACTIVE 220 00:14:02,209 --> 00:14:04,676 HUNDREDS OF MILLIONS OF YEARS AGO 221 00:14:04,678 --> 00:14:09,147 TO STOP ALL STAR FORMATION IN OUR GALAXY. 222 00:14:09,149 --> 00:14:13,017 SAGITTARIUS A-STAR WASN'T ACTIVE AT THAT TIME, 223 00:14:13,019 --> 00:14:15,920 SO IT'S NO LONGER A SUSPECT. 224 00:14:17,991 --> 00:14:21,359 THE HUNT IS ON FOR A DIFFERENT GALAXY KILLER, 225 00:14:21,361 --> 00:14:25,630 AND SCIENTISTS ARE WIDENING THE INVESTIGATION. 226 00:14:25,632 --> 00:14:28,199 MAYBE THE KILLER ISN'T INSIDE OUR GALAXY. 227 00:14:28,201 --> 00:14:31,402 IT COULD BE THAT WE SUFFERED A HIT-AND-RUN. 228 00:14:31,404 --> 00:14:38,676 ♪♪ 229 00:14:39,913 --> 00:14:49,654 IT COULD BE THAT WE SUFFERED A HIT-AND-RUN. 230 00:14:49,656 --> 00:14:53,091 ♪♪ 231 00:14:53,093 --> 00:14:55,693 Narrator: OUR UNIVERSE IS A CRIME SCENE. 232 00:14:57,998 --> 00:15:03,134 STAR PRODUCTION IN THE MILKY WAY IS BREAKING DOWN. 233 00:15:03,136 --> 00:15:05,236 OUR GALAXY IS DYING, 234 00:15:05,238 --> 00:15:08,873 AND ASTRONOMERS ARE EXAMINING THE BODY FOR CLUES. 235 00:15:11,111 --> 00:15:16,681 THE MILKY WAY'S DISK IS MADE UP OF THREE SECTIONS -- 236 00:15:16,683 --> 00:15:21,386 A NUCLEUS, HOME TO THE GALAXY'S SUPERMASSIVE BLACK HOLE... 237 00:15:24,291 --> 00:15:29,594 ...A DENSE, CENTRAL BULGE 10,000 LIGHT-YEARS ACROSS, 238 00:15:29,596 --> 00:15:31,262 AND THE SPIRAL ARMS -- 239 00:15:31,264 --> 00:15:35,099 FULL OF GAS, DUST, AND BILLIONS OF STARS. 240 00:15:37,170 --> 00:15:41,873 THE SPIRAL ARMS SHOULD BE FLAT, BUT THEY'RE RIPPLING. 241 00:15:41,875 --> 00:15:45,143 IS THIS A CLUE FOR THE COSMIC DETECTIVES? 242 00:15:46,947 --> 00:15:48,980 Bullock: TODAY, WE LOOK AT THE EDGE OF THE MILKY WAY, 243 00:15:48,982 --> 00:15:51,049 AND WE SEE MYSTERIOUS RIPPLES IN ITS GAS, 244 00:15:51,051 --> 00:15:53,251 AND WE WONDER, WHAT'S THE ORIGIN? 245 00:15:53,253 --> 00:15:55,353 SOMETHING MUST HAVE CAUSED IT TO HAPPEN. 246 00:15:55,355 --> 00:15:57,822 SOMETHING LIKE THAT JUST DOESN'T HAPPEN ON ITS OWN. 247 00:15:57,824 --> 00:15:59,724 THE REAL QUESTION IS, WHY? 248 00:16:04,331 --> 00:16:08,900 Narrator: WHATEVER CAUSED THE RIPPLES DIDN'T HANG AROUND. 249 00:16:08,902 --> 00:16:11,936 IS THIS EVIDENCE OF A GALACTIC HIT-AND-RUN? 250 00:16:15,008 --> 00:16:17,175 JANUARY 2016. 251 00:16:20,146 --> 00:16:24,182 ASTRONOMERS STUDYING DATA FROM THE VISTA TELESCOPE 252 00:16:24,184 --> 00:16:26,184 DISCOVER SOMETHING INCREDIBLE... 253 00:16:30,290 --> 00:16:32,824 ...THREE NEARBY STARS. 254 00:16:32,826 --> 00:16:35,560 ON THEIR OWN, NOTHING SPECIAL, 255 00:16:35,562 --> 00:16:39,163 EXCEPT THEY'VE RECENTLY LEFT OUR GALAXY, 256 00:16:39,165 --> 00:16:43,735 AND THEY'RE TRAVELING AT 350,000 MILES AN HOUR. 257 00:16:47,507 --> 00:16:49,941 SO, WE'VE DISCOVERED THESE STARS THAT ARE CAREENING 258 00:16:49,943 --> 00:16:52,710 OUT OF THE GALAXY AT SUPER-HIGH VELOCITIES. 259 00:16:52,712 --> 00:16:54,979 COULD THESE THREE STARS SOMEHOW BE RESPONSIBLE 260 00:16:54,981 --> 00:16:56,881 FOR WARPING THE MILKY WAY'S DISK? 261 00:16:56,883 --> 00:16:58,349 WELL, ABSOLUTELY NOT. 262 00:16:58,351 --> 00:17:01,586 THE MILKY WAY IS SO MUCH MORE MASSIVE THAN JUST THREE STARS. 263 00:17:01,588 --> 00:17:04,989 THREE STARS ALONE CAN'T WARP A GALAXY, 264 00:17:04,991 --> 00:17:08,359 BUT THOSE THREE STARS CAN BE INDICATIVE OF MORE STARS. 265 00:17:08,361 --> 00:17:10,862 THEY CAN BE INDICATIVE OF THE PRESENCE OF, SAY, 266 00:17:10,864 --> 00:17:14,065 A DWARF GALAXY, AND THAT CAN WARP THE GALAXY. 267 00:17:16,036 --> 00:17:19,470 Narrator: DWARF GALAXIES ARE ABUNDANT. 268 00:17:19,472 --> 00:17:22,774 BUT A TINY FRACTION OF THE SIZE OF A MAJOR GALAXY, 269 00:17:22,776 --> 00:17:24,342 LIKE THE MILKY WAY. 270 00:17:26,413 --> 00:17:29,781 SO THEY'RE DIFFICULT TO DETECT. 271 00:17:29,783 --> 00:17:33,985 BUT THESE THREE BRIGHT STARS SHOW THERE'S A DWARF GALAXY 272 00:17:33,987 --> 00:17:38,289 HIDING BEYOND THE EDGE OF THE MILKY WAY. 273 00:17:38,291 --> 00:17:41,426 AND SCIENTISTS CAN STUDY THE TRIO OF STARS 274 00:17:41,428 --> 00:17:43,161 TO REWIND THE CLOCK 275 00:17:43,163 --> 00:17:47,365 AND TRACK BACK THE PAST MOVEMENTS OF THE DWARF GALAXY. 276 00:17:50,236 --> 00:17:53,037 SIMULATIONS SUGGEST THAT MILLIONS OF YEARS AGO, 277 00:17:53,039 --> 00:17:54,305 THIS DWARF GALAXY 278 00:17:54,307 --> 00:17:56,374 PUNCHED THROUGH THE PLANE OF THE MILKY WAY. 279 00:18:01,314 --> 00:18:06,084 Narrator: AS THE FAST-MOVING DWARF GALAXY HURTLES TOWARDS THE MILKY WAY, 280 00:18:06,086 --> 00:18:11,823 MILLIONS OF STARS SEEM SET ON A COLLISION COURSE. 281 00:18:11,825 --> 00:18:14,158 CATASTROPHE LOOKS INEVITABLE. 282 00:18:16,062 --> 00:18:19,063 BUT APPEARANCES CAN BE DECEPTIVE. 283 00:18:20,934 --> 00:18:23,401 WHEN GALAXIES COLLIDE, THE FIRST THING YOU MIGHT IMAGINE 284 00:18:23,403 --> 00:18:26,037 IS THAT THE STARS COLLIDE, BUT ACTUALLY, THAT DOESN'T HAPPEN. 285 00:18:26,039 --> 00:18:27,839 GALAXIES ARE MOSTLY EMPTY SPACE. 286 00:18:27,841 --> 00:18:30,041 IF YOU TOOK THE SUN, WHICH IS REALLY BIG -- 287 00:18:30,043 --> 00:18:31,776 IT'S A MILLION MILES ACROSS -- 288 00:18:31,778 --> 00:18:35,746 AND SHRUNK IT DOWN TO THE SIZE OF A PIECE OF POLLEN, 289 00:18:35,748 --> 00:18:39,117 THE GALAXY ITSELF WOULD BE TWICE THE SIZE OF THE PACIFIC OCEAN, 290 00:18:39,119 --> 00:18:42,587 AND THE NEAREST STAR TO THE SUN WOULD BE A MILE AWAY. 291 00:18:42,589 --> 00:18:45,756 THOSE TINY PIECES OF POLLEN ARE NEVER GOING TO HIT EACH OTHER. 292 00:18:49,696 --> 00:18:53,831 Narrator: THE DISTANCES INVOLVED ARE STAGGERING. 293 00:18:53,833 --> 00:18:55,500 AND AT THE MOMENT OF IMPACT, 294 00:18:55,502 --> 00:18:58,069 MOST OF THE STARS FROM THE TWO GALAXIES 295 00:18:58,071 --> 00:19:00,705 MISS EACH OTHER ENTIRELY. 296 00:19:00,707 --> 00:19:04,742 BUT THAT DOESN'T MEAN THE MILKY WAY IS SAFE. 297 00:19:06,913 --> 00:19:09,680 Sutter: EVEN THOUGH THE STARS JUST PASS EACH OTHER, 298 00:19:09,682 --> 00:19:13,518 THEY DO GRAVITATIONALLY INTERACT AS THEY COME CLOSE, 299 00:19:13,520 --> 00:19:16,888 AND THIS GRAVITATIONAL INTERACTION SETS THEM 300 00:19:16,890 --> 00:19:18,489 ON A COURSE THAT IS DIFFERENT 301 00:19:18,491 --> 00:19:20,925 THAN IF THEY WERE TO LIVE BY THEMSELVES. 302 00:19:23,763 --> 00:19:25,863 Bullock: IN MUCH THE SAME WAY THAT TAKING A STONE 303 00:19:25,865 --> 00:19:27,532 AND DROPPING IT INTO A STILL POND 304 00:19:27,534 --> 00:19:29,667 CREATES RIPPLES IN THE WATER, 305 00:19:29,669 --> 00:19:32,336 A GALAXY LIKE THIS SLAMMING INTO THE MILKY WAY 306 00:19:32,338 --> 00:19:34,739 CAN CREATE RIPPLE EFFECTS THROUGHOUT THE DISK. 307 00:19:38,044 --> 00:19:39,710 Narrator: THE RIPPLES IN THE MILKY WAY 308 00:19:39,712 --> 00:19:43,114 STRETCH ACROSS TENS OF THOUSANDS OF LIGHT-YEARS. 309 00:19:45,285 --> 00:19:50,621 STILL, THIS HIT-AND-RUN ISN'T ENOUGH TO KILL THE MILKY WAY. 310 00:19:50,623 --> 00:19:54,292 IT ONLY CAUSES A FLESH WOUND. 311 00:19:54,294 --> 00:19:59,797 BUT WHAT IF THIS DWARF GALAXY ISN'T ACTING ALONE? 312 00:19:59,799 --> 00:20:01,766 WHAT IF IT HAS ACCOMPLICES? 313 00:20:04,304 --> 00:20:07,038 THERE ARE A LOT OF DWARF GALAXIES OUT THERE, 314 00:20:07,040 --> 00:20:10,308 AND IT TURNS OUT COLLISIONS BETWEEN THESE DWARF GALAXIES 315 00:20:10,310 --> 00:20:13,177 AND BIG GALAXIES, LIKE THE MILKY WAY, ARE COMMON. 316 00:20:13,179 --> 00:20:14,445 THEY HAPPEN ALL THE TIME. 317 00:20:14,447 --> 00:20:16,480 RIGHT NOW, THERE ARE SEVERAL DWARF GALAXIES 318 00:20:16,482 --> 00:20:18,516 THAT THE MILKY WAY IS SWALLOWING UP. 319 00:20:18,518 --> 00:20:20,718 IN FACT, A REALLY FUN THING IS THAT WE'RE ACTUALLY CLOSER 320 00:20:20,720 --> 00:20:22,887 TO THE CORE OF ONE OF THESE GALAXIES -- 321 00:20:22,889 --> 00:20:24,822 THE CANIS MAJORIS DWARF GALAXY -- 322 00:20:24,824 --> 00:20:26,657 THAN WE ARE TO THE CORE OF THE MILKY WAY. 323 00:20:26,659 --> 00:20:29,594 SO SOME OF THE STARS THAT YOU SEE AROUND YOU IN THE NIGHT SKY 324 00:20:29,596 --> 00:20:32,330 ARE ACTUALLY STARS FROM A DIFFERENT GALAXY. 325 00:20:32,332 --> 00:20:35,433 SO, WHAT HAPPENS WHEN ALL THESE DWARF GALAXIES COME TOGETHER 326 00:20:35,435 --> 00:20:38,302 AND START PULLING AND TUGGING ON A LARGER GALAXY? 327 00:20:38,304 --> 00:20:44,108 ♪♪ 328 00:20:44,110 --> 00:20:47,945 Narrator: COSMOLOGISTS BELIEVE THERE COULD BE HUNDREDS OF DWARF GALAXIES 329 00:20:47,947 --> 00:20:50,481 SURROUNDING THE MILKY WAY. 330 00:20:53,319 --> 00:20:56,821 A COLLISION WITH JUST ONE OF THESE DWARF GALAXIES 331 00:20:56,823 --> 00:21:00,558 MAY HAVE RIPPLED THE MILKY WAY'S SPIRAL ARMS, 332 00:21:02,562 --> 00:21:05,763 BUT A GANG OF DWARF GALAXIES 333 00:21:05,765 --> 00:21:11,269 COULD HAVE A FAR BIGGER AND FAR MORE DEADLY EFFECT. 334 00:21:11,271 --> 00:21:13,571 DWARF GALAXIES AND THE WAY THEY INTERACT WITH BIG GALAXIES, 335 00:21:13,573 --> 00:21:14,805 LIKE THE MILKY WAY, 336 00:21:14,807 --> 00:21:17,775 CAN INFLECT TREMENDOUS CHANGE IN OUR UNIVERSE. 337 00:21:17,777 --> 00:21:20,411 WHEN THEY SLAM INTO A GALAXY, THEY CAN CHANGE ITS STRUCTURE. 338 00:21:20,413 --> 00:21:23,247 THE MILKY WAY WOULD NOT LOOK ANYTHING LIKE IT LOOKS TODAY 339 00:21:23,249 --> 00:21:26,284 WITHOUT THOSE DWARF GALAXIES. 340 00:21:26,286 --> 00:21:29,020 Narrator: REPEATED DWARF-GALAXY COLLISIONS 341 00:21:29,022 --> 00:21:32,723 COULD HAVE RADICALLY ALTERED THE SHAPE OF THE MILKY WAY ITSELF. 342 00:21:35,328 --> 00:21:39,096 THEIR GRAVITATIONAL DISRUPTIONS COULD HAVE CREATED A DISTINCTIVE 343 00:21:39,098 --> 00:21:43,167 AND POSSIBLY FATAL FEATURE IN THE MIDDLE OF OUR GALAXY -- 344 00:21:43,169 --> 00:21:44,669 THE GALACTIC BAR. 345 00:21:48,074 --> 00:21:50,341 THE CENTER OF THE MILKY WAY IS ELONGATED. 346 00:21:50,343 --> 00:21:52,243 INSTEAD OF IT BEING SHAPED LIKE A SPHERE, 347 00:21:52,245 --> 00:21:55,413 IT'S MORE SHAPED LIKE A BAR, AND THE BAR IS MADE BY STARS 348 00:21:55,415 --> 00:21:59,550 ACTUALLY ORBITING IN THIS SORT OF ELONGATED WAY. 349 00:21:59,552 --> 00:22:02,420 Oluseyi: AND THIS BAR CAN BE BAD FOR THE HEALTH OF THE GALAXY 350 00:22:02,422 --> 00:22:04,989 BECAUSE WHAT THEY DO IS HELP TO FUNNEL GAS 351 00:22:04,991 --> 00:22:06,824 INTO THE CORE OF THE GALAXY. 352 00:22:06,826 --> 00:22:11,228 THE LOSS OF THIS GAS COULD BE A WAY OF STOPPING STAR FORMATION. 353 00:22:14,701 --> 00:22:17,902 Narrator: THE BAR-SHAPED BULGE AT THE CENTER OF THE MILKY WAY 354 00:22:17,904 --> 00:22:20,871 SWEEPS OUR GALAXY'S STAR-BUILDING GAS 355 00:22:20,873 --> 00:22:23,107 INTO THE GALACTIC NUCLEUS. 356 00:22:23,109 --> 00:22:24,709 HERE, IT GETS GOBBLED UP 357 00:22:24,711 --> 00:22:27,545 BY OUR GALAXY'S SUPERMASSIVE BLACK HOLE. 358 00:22:31,617 --> 00:22:35,786 WITHOUT THE STAR-BUILDING MATERIAL, NO NEW STARS CAN FORM, 359 00:22:35,788 --> 00:22:39,223 AND THE GALAXY DIES. 360 00:22:39,225 --> 00:22:41,258 SO, IS IT CASE CLOSED? 361 00:22:41,260 --> 00:22:43,828 ARE DWARF GALAXIES KILLING THE MILKY WAY? 362 00:22:43,830 --> 00:22:47,865 IS THE MURDER WEAPON A GALACTIC BAR? 363 00:22:47,867 --> 00:22:50,735 SO, IT'S POSSIBLE THAT THE FORMATION OF THESE BARS 364 00:22:50,737 --> 00:22:54,438 HELPS TURN OFF STAR FORMATION IN THE VERY CORE OF THE GALAXY, 365 00:22:54,440 --> 00:22:57,341 BUT THAT'S JUST THE CENTRAL REGIONS OF THE GALAXY. 366 00:22:57,343 --> 00:22:59,210 THAT DOESN'T EXPLAIN WHAT'S GOING FARTHER OUT 367 00:22:59,212 --> 00:23:01,045 IN THE SPIRAL ARMS. 368 00:23:01,047 --> 00:23:04,548 SO, IF STAR FORMATION REALLY IS SHUTTING DOWN IN THE MILKY WAY, 369 00:23:04,550 --> 00:23:06,851 IT'S NOT REALLY THE FAULT OF THE BAR. 370 00:23:09,021 --> 00:23:13,391 Narrator: DWARF GALAXIES CAUSE THE MILKY WAY GRIEVOUS BODILY HARM 371 00:23:13,393 --> 00:23:16,460 BY CREATING THE GALACTIC BAR. 372 00:23:16,462 --> 00:23:21,899 BUT THEY'RE OFF THE HOOK FOR ATTEMPTED GALACTIC MURDER. 373 00:23:21,901 --> 00:23:24,635 THE INVESTIGATION CONTINUES, 374 00:23:24,637 --> 00:23:29,840 AND IT COULD BE ABOUT TO TAKE A DRAMATIC TWIST. 375 00:23:29,842 --> 00:23:32,109 IT MIGHT NOT BE THAT THE GALAXY'S BEING MURDERED. 376 00:23:32,111 --> 00:23:34,412 IT COULD JUST BE EATING ITSELF TO DEATH. 377 00:23:34,414 --> 00:23:44,121 ♪♪ 378 00:23:45,491 --> 00:23:54,532 ♪ IT COULD JUST BE EATING ITSELF TO DEATH. 379 00:23:54,534 --> 00:23:58,536 Narrator: THE MILKY WAY IS BEING KILLED OFF. 380 00:23:58,538 --> 00:24:01,305 AND THE PERPETRATOR REMAINS AT LARGE. 381 00:24:03,476 --> 00:24:05,443 SCIENTISTS INVESTIGATING THE CRIME 382 00:24:05,445 --> 00:24:07,178 ARE RUNNING OUT OF SUSPECTS. 383 00:24:09,215 --> 00:24:11,348 BUT THE HUNT FOR CLUES CONTINUES, 384 00:24:13,319 --> 00:24:18,556 SO ASTRONOMERS ARE EXAMINING THE DYING BODY OF THE MILKY WAY. 385 00:24:18,558 --> 00:24:21,725 OUR GALAXY IS A HAZY DISK OF STARS 386 00:24:21,727 --> 00:24:25,296 SURROUNDED BY A HALO OF SUPERHEATED GAS. 387 00:24:27,166 --> 00:24:31,135 IT'S OVER 100,000 LIGHT-YEARS ACROSS. 388 00:24:31,137 --> 00:24:33,304 BUT IT HASN'T ALWAYS BEEN SO BIG. 389 00:24:35,575 --> 00:24:37,775 WHEN YOU THINK ABOUT THINGS SO VAST, 390 00:24:37,777 --> 00:24:39,810 SO GIGANTIC AND ANCIENT AS GALAXIES, 391 00:24:39,812 --> 00:24:41,278 YOU'RE KIND OF TEMPTED TO THINK 392 00:24:41,280 --> 00:24:42,847 THAT THEY'RE VERY STABLE OBJECTS, 393 00:24:42,849 --> 00:24:44,815 THAT THEY DON'T CHANGE MUCH OVER TIME, 394 00:24:44,817 --> 00:24:46,617 BUT WE NOW KNOW THAT OUR OWN GALAXY 395 00:24:46,619 --> 00:24:48,552 IS THE PRODUCT OF MANY SMALLER GALAXIES 396 00:24:48,554 --> 00:24:50,354 THAT CAME TOGETHER OVER TIME, 397 00:24:50,356 --> 00:24:53,057 AND THERE ARE OTHER GALAXIES STILL COLLIDING WITH US. 398 00:24:56,028 --> 00:24:58,295 Plait: WE SEE GALAXIES EATING EACH OTHER ALL THE TIME. 399 00:24:58,297 --> 00:25:00,998 THEY COLLIDE, AND IF ONE GALAXY IS VERY BIG 400 00:25:01,000 --> 00:25:02,867 AND ONE GALAXY IS VERY SMALL, 401 00:25:02,869 --> 00:25:06,136 THE LITTLE GALAXY FALLS INTO THE BIG ONE, GETS TORN APART, 402 00:25:06,138 --> 00:25:10,241 AND BECOMES A PART OF THAT BIGGER GALAXY. 403 00:25:10,243 --> 00:25:12,576 Narrator: THE MILKY WAY MIGHT BE DYING, 404 00:25:12,578 --> 00:25:16,046 BUT IT'S STILL A MONSTER FORAGING THROUGH THE UNIVERSE, 405 00:25:16,048 --> 00:25:18,415 SWALLOWING SMALLER GALAXIES WHOLE. 406 00:25:21,988 --> 00:25:24,054 IT CONSUMES THEIR STARS. 407 00:25:24,056 --> 00:25:28,125 BUT IT ALSO HAS A TASTE FOR THEIR STAR-BUILDING GAS. 408 00:25:29,996 --> 00:25:33,330 AND IT DOESN'T HAVE TO COLLIDE WITH OTHER GALAXIES 409 00:25:33,332 --> 00:25:36,667 TO FEED OFF OF THEM. 410 00:25:36,669 --> 00:25:39,470 NOW, THE LIFEBLOOD OF A GALAXY IS HYDROGEN GAS. 411 00:25:39,472 --> 00:25:41,739 THAT'S WHAT ACTUALLY CREATES NEW STARS. 412 00:25:41,741 --> 00:25:44,708 SO AS A DWARF GALAXY PASSES BY THE MILKY WAY, 413 00:25:44,710 --> 00:25:47,912 THE TREMENDOUSLY MASSIVE HALO OF THE MILKY WAY, 414 00:25:47,914 --> 00:25:51,282 ALL OF THAT GAS, CAN DRAW OFF MATERIAL FROM THE DWARF GALAXY, 415 00:25:51,284 --> 00:25:53,350 ADDING IT TO THE MILKY WAY. 416 00:25:53,352 --> 00:25:55,586 SO IN THIS WAY, THE MILKY WAY DRAINS AWAY 417 00:25:55,588 --> 00:25:58,622 THE LIFEBLOOD OF OTHER GALAXIES. 418 00:25:58,624 --> 00:26:01,191 IN SOME SENSE, YOU COULD SAY IT'S A VAMPIRE 419 00:26:01,193 --> 00:26:03,994 BECAUSE A VAMPIRE SUCKS THE LIFE OUT OF OTHER THINGS 420 00:26:03,996 --> 00:26:05,429 SO IT CAN REMAIN YOUNG. 421 00:26:09,368 --> 00:26:16,674 Narrator: IN ITS 13 BILLION-YEAR LIFE, OUR VAMPIRE GALAXY HAS FEASTED. 422 00:26:16,676 --> 00:26:19,944 CONSUMING THE LIFEBLOOD OF ITS GALACTIC VICTIMS, 423 00:26:19,946 --> 00:26:22,780 THE MILKY WAY HAS GROWN FAT. 424 00:26:25,217 --> 00:26:28,352 BUT COULD THIS MONSTROUS FEEDING FRENZY BE A FACTOR 425 00:26:28,354 --> 00:26:30,187 IN THE MILKY WAY'S DEMISE? 426 00:26:33,092 --> 00:26:34,992 ONCE AGAIN, CRUCIAL EVIDENCE 427 00:26:34,994 --> 00:26:39,597 COMES FROM THE SLOAN DIGITAL SKY SURVEY. 428 00:26:39,599 --> 00:26:42,666 THEIR TELESCOPE MAPS THE STARS IN OUR GALAXY, 429 00:26:42,668 --> 00:26:46,470 BUT IT ALSO MAPS THE GALAXIES IN OUR UNIVERSE. 430 00:26:48,941 --> 00:26:54,445 LOOKING AT DISTANT GALAXIES IS LIKE LOOKING BACK IN TIME. 431 00:26:54,447 --> 00:26:56,847 BECAUSE THE FARTHER AWAY THEY ARE, 432 00:26:56,849 --> 00:26:59,617 THE LONGER THEIR LIGHT TAKES TO REACH US. 433 00:27:02,488 --> 00:27:07,424 WE SEE THE MOST DISTANT GALAXIES NOT AS THEY ARE NOW, 434 00:27:07,426 --> 00:27:12,096 BUT AS THEY WERE -- BILLIONS OF YEARS AGO. 435 00:27:12,098 --> 00:27:13,530 SO, WHEN YOU LOOK AT THESE GALAXIES, 436 00:27:13,532 --> 00:27:15,799 YOU'RE SEEING THEM AS THEY WERE WHEN THEY WERE VERY YOUNG, 437 00:27:15,801 --> 00:27:18,802 AND YOU'RE SEEING THESE GALAXIES AS THEY ARE MORE RECENTLY, 438 00:27:18,804 --> 00:27:21,171 SO YOU CAN ACTUALLY LOOK AT THE EVOLUTION -- 439 00:27:21,173 --> 00:27:25,075 HOW GALAXIES CHANGE OVER TIME AS THE UNIVERSE AGES. 440 00:27:27,213 --> 00:27:28,779 Narrator: WHILE STUDYING THE DATA, 441 00:27:28,781 --> 00:27:31,782 SCIENTISTS MAKE A DRAMATIC DISCOVERY. 442 00:27:31,784 --> 00:27:36,353 THEY FIND SPIRAL GALAXIES, JUST LIKE THE MILKY WAY, 443 00:27:36,355 --> 00:27:40,090 DYING ALL OVER THE UNIVERSE. 444 00:27:40,092 --> 00:27:42,926 AND WHAT CONNECTS THEM IS THEIR MASS. 445 00:27:44,964 --> 00:27:46,530 THERE SEEMS TO BE AN UPPER WEIGHT LIMIT 446 00:27:46,532 --> 00:27:49,366 FOR THE SIZES OF SPIRAL GALAXIES. 447 00:27:49,368 --> 00:27:51,835 UP TO ABOUT A TRILLION TIMES THE MASS OF THE SUN, 448 00:27:51,837 --> 00:27:54,738 WE SEE SPIRAL GALAXIES THAT CONTINUE TO FORM STARS, 449 00:27:54,740 --> 00:27:56,707 BUT ONCE THEY PASS THIS THRESHOLD, 450 00:27:56,709 --> 00:27:59,109 GALAXIES TEND TO DIE AND RUN OUT OF STARS. 451 00:28:01,280 --> 00:28:03,380 Narrator: WHILE DEVOURING THE STAR-BUILDING GAS 452 00:28:03,382 --> 00:28:05,582 OF SMALLER GALAXIES, 453 00:28:05,584 --> 00:28:08,686 THE MILKY WAY MAY HAVE GROWN OBESE, 454 00:28:08,688 --> 00:28:12,690 AND NOW IT COULD BE CHOKING TO DEATH ON ITS OWN DINNER. 455 00:28:12,692 --> 00:28:14,958 BUT HOW? 456 00:28:14,960 --> 00:28:17,661 ONCE A SPIRAL GALAXY IS SUFFICIENTLY BIG, 457 00:28:17,663 --> 00:28:20,264 IT'S GOING TO HAVE AN INCREDIBLE GRAVITATIONAL FORCE, 458 00:28:20,266 --> 00:28:22,666 SO ANY GAS THAT IT PULLS TO ITSELF 459 00:28:22,668 --> 00:28:26,236 IS GOING TO COME IN AT AN INCREDIBLY HIGH SPEED. 460 00:28:26,238 --> 00:28:28,439 THAT GAS IS GOING TO BE SUPERHEATED. 461 00:28:32,344 --> 00:28:34,978 Narrator: THE SUPERHEATED GAS MOVES SO QUICKLY 462 00:28:34,980 --> 00:28:39,083 THAT IT'S PREVENTED FROM FALLING INTO THE MILKY WAY. 463 00:28:39,085 --> 00:28:44,254 THE GAS IS TOO ENERGETIC FOR OUR GALAXY'S GRAVITY TO PULL IT IN. 464 00:28:44,256 --> 00:28:48,459 INSTEAD, IT STAYS IN THE HALO AROUND THE MILKY WAY, 465 00:28:48,461 --> 00:28:53,197 AND OUR GALAXY'S FOOD SUPPLY IS CHOKED OFF. 466 00:28:53,199 --> 00:28:57,634 EVENTUALLY, OUR GALAXY WILL STARVE. 467 00:28:57,636 --> 00:28:59,536 THIS WILL ONLY HAPPEN IF THE MILKY WAY 468 00:28:59,538 --> 00:29:02,973 IS OVER THE STAR-BUILDING WEIGHT LIMIT. 469 00:29:02,975 --> 00:29:07,511 BUT HOW EXACTLY DO YOU WEIGH A GALAXY? 470 00:29:07,513 --> 00:29:09,980 ONE BASIC WAY WE CAN WEIGH A GALAXY 471 00:29:09,982 --> 00:29:12,683 IS MEASURE HOW FAST THE STARS ARE MOVING WITHIN IT. 472 00:29:12,685 --> 00:29:15,619 SO THE FASTER THE STARS ORBIT AROUND THE CENTER OF THE GALAXY, 473 00:29:15,621 --> 00:29:18,489 THE MORE MASSIVE THE GALAXY IS. 474 00:29:18,491 --> 00:29:22,793 Narrator: THIS METHOD OF WEIGHING THE MILKY WAY RELIES ON GRAVITY. 475 00:29:22,795 --> 00:29:26,063 FAST-MOVING STARS NEED MORE GRAVITY TO HOLD THEM 476 00:29:26,065 --> 00:29:27,397 IN THEIR ORBITS, 477 00:29:27,399 --> 00:29:32,269 AND MORE GRAVITY MEANS MORE GALACTIC MASS. 478 00:29:32,271 --> 00:29:36,373 WHEN SCIENTISTS USE THIS INFORMATION TO RUN THE MATH, 479 00:29:36,375 --> 00:29:39,910 THE HORRIBLE TRUTH IS REVEALED. 480 00:29:39,912 --> 00:29:42,613 Thaller: WE'VE PASSED KIND OF A CRITICAL LEVEL. 481 00:29:42,615 --> 00:29:46,183 THE MILKY WAY IS FAR TOO MASSIVE FOR ITS OWN HEALTH, 482 00:29:46,185 --> 00:29:49,019 AND WE'VE ENTERED THE BEGINNING OF THE END. 483 00:29:49,021 --> 00:29:52,222 Plait: WE'RE RUNNING OUT OF GAS, AND I MEAN THIS LITERALLY. 484 00:29:52,224 --> 00:29:54,091 GAS CLOUDS FORM STARS, 485 00:29:54,093 --> 00:29:57,528 AND AS THEY FORM STARS, THEY'RE USED UP, 486 00:29:57,530 --> 00:29:59,763 AND SO OUR GAS TANK IS GETTING CLOSER AND CLOSER 487 00:29:59,765 --> 00:30:02,266 TO EMPTY EVERY DAY. 488 00:30:06,038 --> 00:30:09,072 Narrator: THE INVESTIGATION INTO THE KILLING OF THE MILKY WAY 489 00:30:09,074 --> 00:30:10,440 IS CLOSED. 490 00:30:12,645 --> 00:30:14,011 THE VERDICT? 491 00:30:14,013 --> 00:30:17,815 THE GREEDY MILKY WAY IS KILLING ITSELF. 492 00:30:20,452 --> 00:30:24,454 OVER MILLIONS OF YEARS, STAR FORMATION GRINDS TO A HALT, 493 00:30:24,456 --> 00:30:26,356 AND THE GALAXY DIES. 494 00:30:28,994 --> 00:30:34,131 BUT COULD THE GALAXY BE RESURRECTED? 495 00:30:34,133 --> 00:30:35,999 WE SEEM TO BE TELLING A VERY SAD STORY. 496 00:30:36,001 --> 00:30:38,202 WE'RE TALKING ABOUT THE DEMISE OF THE MILKY WAY GALAXY -- 497 00:30:38,204 --> 00:30:39,970 THE END OF STAR FORMATION -- 498 00:30:39,972 --> 00:30:41,805 BUT MAYBE IT'S JUST A LITTLE BIT TOO SOON 499 00:30:41,807 --> 00:30:43,574 TO WRITE THE DEATH ANNOUNCEMENT YET. 500 00:30:43,576 --> 00:30:46,076 HOPE COULD BE JUST OVER THE HORIZON. 501 00:30:48,914 --> 00:30:52,149 IN SPACE AND ASTROPHYSICS, REALLY ANYTHING IS POSSIBLE. 502 00:30:52,151 --> 00:30:58,355 ♪♪ 503 00:30:59,758 --> 00:31:08,165 ♪ IN SPACE AND ASTROPHYSICS, REALLY ANYTHING IS POSSIBLE. 504 00:31:08,167 --> 00:31:12,936 Narrator: THE SHOCKING CASE OF OUR DYING GALAXY HAS BEEN SOLVED. 505 00:31:12,938 --> 00:31:15,272 THERE WAS NO KILLER. 506 00:31:15,274 --> 00:31:18,942 TURNS OUT, THE MILKY WAY IS EATING ITSELF TO DEATH. 507 00:31:23,182 --> 00:31:26,650 BUT IS THIS REALLY THE END? 508 00:31:26,652 --> 00:31:29,620 COULD SALVATION BE HEADING OUR WAY? 509 00:31:31,523 --> 00:31:33,390 EVEN IF STAR FORMATION IS TURNING OFF 510 00:31:33,392 --> 00:31:34,758 IN THE MILKY WAY NOW, 511 00:31:34,760 --> 00:31:36,560 WE KNOW THAT IT'S ON A COLLISION COURSE 512 00:31:36,562 --> 00:31:38,528 WITH THE ANDROMEDA GALAXY. 513 00:31:38,530 --> 00:31:39,696 THEY'RE MOVING TOWARD EACH OTHER 514 00:31:39,698 --> 00:31:44,001 AT HUNDREDS OF THOUSANDS OF MILES PER HOUR. 515 00:31:44,003 --> 00:31:45,502 A COLLISION SOUNDS LIKE SOMETHING 516 00:31:45,504 --> 00:31:47,037 THAT'S ALWAYS DESTRUCTIVE, 517 00:31:47,039 --> 00:31:49,039 BUT THAT'S NOT NECESSARILY THE CASE. 518 00:31:51,977 --> 00:31:53,176 Narrator: THE MILKY WAY'S COLLISION 519 00:31:53,178 --> 00:31:57,114 WITH OUR GIANT GALACTIC NEIGHBOR ANDROMEDA 520 00:31:57,116 --> 00:32:00,284 WON'T HAPPEN FOR ANOTHER 4 BILLION YEARS. 521 00:32:02,621 --> 00:32:06,256 BY THEN, STAR FORMATION IN BOTH OF THESE GALAXIES 522 00:32:06,258 --> 00:32:07,958 WILL HAVE STOPPED COMPLETELY. 523 00:32:10,729 --> 00:32:14,731 BUT A GIANT MEET-UP COULD CHANGE ALL THAT. 524 00:32:18,003 --> 00:32:19,469 Sutter: AS AN ISOLATED GALAXY, 525 00:32:19,471 --> 00:32:22,873 THE MILKY WAY IS ALREADY IN ITS WIND-DOWN PHASE. 526 00:32:22,875 --> 00:32:26,543 IT'S NOT PRODUCING AS MANY NEW STARS AS IT USED TO. 527 00:32:26,545 --> 00:32:30,714 BUT THERE IS ONE WAY TO GENERATE A NEW ROUND OF STAR FORMATION, 528 00:32:30,716 --> 00:32:34,418 AND THAT'S THROUGH A GALACTIC MERGER EVENT. 529 00:32:34,420 --> 00:32:36,386 Plait: WHEN ANDROMEDA GETS CLOSE ENOUGH, 530 00:32:36,388 --> 00:32:38,488 THE MUTUAL GRAVITY BETWEEN THE TWO GALAXIES 531 00:32:38,490 --> 00:32:42,793 WILL START TO STRETCH THEM OUT, PULLING THEM OUT LIKE TAFFY. 532 00:32:42,795 --> 00:32:45,729 STARS WILL BE PULLED OUT INTO THESE LONG, LOOPING STREAMERS, 533 00:32:45,731 --> 00:32:46,863 AND THEN THE GALAXIES 534 00:32:46,865 --> 00:32:50,033 WILL PHYSICALLY PASS THROUGH EACH OTHER. 535 00:32:50,035 --> 00:32:53,804 EVENTUALLY, THE TWO GALAXIES WILL DRAW BACK TOGETHER AGAIN 536 00:32:53,806 --> 00:32:56,440 AND MERGE INTO ONE GIGANTIC GALAXY, 537 00:32:56,442 --> 00:32:58,375 AND AT THAT POINT, ALL OF THESE GAS CLOUDS 538 00:32:58,377 --> 00:33:01,545 WILL FLASH INTO STAR FORMATION. 539 00:33:06,251 --> 00:33:10,787 Narrator: AS THE GALAXIES MERGE, THEY'LL BE REBORN. 540 00:33:10,789 --> 00:33:13,757 TWO DYING SPIRAL-SHAPED GALAXIES 541 00:33:13,759 --> 00:33:18,028 BECOME A SINGLE LIVING ELLIPTICAL GALAXY 542 00:33:18,030 --> 00:33:22,032 CALLED MILKOMEDA. 543 00:33:22,034 --> 00:33:24,634 IMAGINE YOU'RE LIVING IN THE FAR FUTURE OF THE GALAXY 544 00:33:24,636 --> 00:33:26,236 AND YOU SEE THE NIGHT SKY 545 00:33:26,238 --> 00:33:28,805 WHILE THE MILKY WAY AND ANDROMEDA ARE COLLIDING. 546 00:33:28,807 --> 00:33:31,108 IT WILL LOOK LIKE A VERY DIFFERENT PLACE. 547 00:33:31,110 --> 00:33:33,343 RATHER THAN ONE BAND ACROSS THE NIGHT SKY, 548 00:33:33,345 --> 00:33:36,079 YOU MIGHT HAVE TWO AS THE TWO DISKS COME TOGETHER. 549 00:33:36,081 --> 00:33:37,748 IT WILL BE A MIRACULOUS SIGHT, 550 00:33:37,750 --> 00:33:40,584 BUT A VERY, VERY DIFFERENT PLACE THAN WE HAVE TODAY. 551 00:33:43,889 --> 00:33:49,059 Narrator: OUR SKY WILL LIGHT UP FOR THE FIRST TIME IN BILLIONS OF YEARS. 552 00:33:49,061 --> 00:33:52,496 STAR FORMATION WILL FLARE ACROSS THE GALAXY. 553 00:33:54,833 --> 00:33:57,734 BUT IS IT TOO SOON TO CELEBRATE? 554 00:34:01,473 --> 00:34:03,840 THIS NEW ROUND OF STAR FORMATION 555 00:34:03,842 --> 00:34:07,677 DURING THE MERGER OF OUR TWO GALAXIES -- 556 00:34:07,679 --> 00:34:10,047 WHILE IT'S VERY COOL FOR A LITTLE BIT, 557 00:34:10,049 --> 00:34:14,785 ONCE IT'S OVER, THAT KIND OF SENDS THE NEW GALAXY 558 00:34:14,787 --> 00:34:16,186 INTO A DEATH SPIRAL. 559 00:34:16,188 --> 00:34:18,955 WHEN NEW STARS ARE BORN IN THIS NEW GALAXY, 560 00:34:18,957 --> 00:34:23,260 MANY OF THEM ARE GOING TO BE HOT, LARGE, BLUE STARS. 561 00:34:23,262 --> 00:34:26,463 EVENTUALLY, THOSE YOUNG, HOT STARS ARE GOING TO START TO DIE, 562 00:34:26,465 --> 00:34:28,565 AND WHEN THEY DO, THEY'RE GOING TO EXPLODE 563 00:34:28,567 --> 00:34:30,567 VIOLENTLY AS SUPERNOVAE. 564 00:34:30,569 --> 00:34:36,039 ♪♪ 565 00:34:36,041 --> 00:34:38,041 AND THOSE SUPERNOVAE ARE GOING TO START 566 00:34:38,043 --> 00:34:40,577 BLASTING GAS OUT OF THE GALAXY. 567 00:34:44,249 --> 00:34:45,782 Bullock: ALL OF THE GAS IS GONE. 568 00:34:45,784 --> 00:34:48,085 THERE'S NO MORE STUFF TO FORM STARS. 569 00:34:48,087 --> 00:34:49,853 AND THAT'S WHAT KILLS A GALAXY. 570 00:34:53,625 --> 00:34:55,926 Narrator: IT'LL TAKE HUNDREDS OF MILLIONS OF YEARS 571 00:34:55,928 --> 00:35:00,530 FOR MILKOMEDA TO RUN OUT OF STAR-BUILDING GAS. 572 00:35:00,532 --> 00:35:04,835 AND THEN OUR NEW ELLIPTICAL GALAXY WILL STARVE. 573 00:35:06,638 --> 00:35:09,239 BUT THE FINAL BLOW IS STILL TO COME. 574 00:35:11,677 --> 00:35:13,910 ANOTHER ISSUE TO CONSIDER IS WHAT HAPPENS 575 00:35:13,912 --> 00:35:15,946 TO THE TWO SUPERMASSIVE BLACK HOLES 576 00:35:15,948 --> 00:35:18,648 AT THE CORES OF THE TWO GALAXIES. 577 00:35:18,650 --> 00:35:21,184 WELL, INITIALLY, THEY'RE GOING TO ORBIT EACH OTHER, 578 00:35:21,186 --> 00:35:25,755 STIRRING UP A LOT OF TURBULENCE, AND THEY'RE GOING TO COMBINE. 579 00:35:25,757 --> 00:35:28,692 AND BECAUSE THERE'S A LOT OF NEW, HOT, FRESH GAS, 580 00:35:28,694 --> 00:35:31,862 OUR NEW GALAXY IS GOING TO BE A QUASAR. 581 00:35:31,864 --> 00:35:34,397 AND THAT QUASAR IS GOING TO TURN UP THE HEAT, 582 00:35:34,399 --> 00:35:36,032 IT'S GOING TO TURN UP THE TURBULENCE, 583 00:35:36,034 --> 00:35:39,269 AND THIS MEANS STAR FORMATION IS GOING TO BE SHUT OFF. 584 00:35:41,540 --> 00:35:45,142 Narrator: THE COMBINED POWER OF THE SUPERMASSIVE BLACK HOLES 585 00:35:45,144 --> 00:35:49,146 HELP CREATE A QUASAR THAT TEARS THROUGH THE GALAXY. 586 00:35:52,251 --> 00:35:55,452 IT RELEASES FEROCIOUS BEAMS OF RADIATION 587 00:35:55,454 --> 00:35:59,022 THAT BLAST THROUGH MILKOMEDA'S STAR-FORMING GAS. 588 00:36:02,361 --> 00:36:04,261 IT'S ONLY JUST BEEN REBORN, 589 00:36:04,263 --> 00:36:08,832 BUT OUR NEWLY ENLARGED GALAXY IS ONCE AGAIN DYING. 590 00:36:11,537 --> 00:36:16,706 VAST GALAXIES, LIKE MILKOMEDA, SEEM DOOMED FROM THE START. 591 00:36:16,708 --> 00:36:20,810 THEIR SIZE CREATES TOO MANY PROBLEMS FOR STAR FORMATION. 592 00:36:23,315 --> 00:36:26,583 OR...SO WE THOUGHT. 593 00:36:26,585 --> 00:36:28,919 THE MORE GALAXIES WE SEE, THE MORE WE REALIZE 594 00:36:28,921 --> 00:36:30,987 THERE'S A LOT OUT THERE WE HAVEN'T DISCOVERED, 595 00:36:30,989 --> 00:36:32,756 AND THERE'S A NEW CLASS OF GALAXIES 596 00:36:32,758 --> 00:36:35,158 ONLY RECENTLY IDENTIFIED. 597 00:36:35,160 --> 00:36:39,763 THESE GALAXIES ARE MORE THAN 10 TIMES THE MASS OF THE MILKY WAY. 598 00:36:39,765 --> 00:36:43,867 AND, INTRIGUINGLY, THEY'RE STILL FORMING STARS. 599 00:36:43,869 --> 00:36:45,602 APPARENTLY WE'VE MISSED SOMETHING. 600 00:36:45,604 --> 00:36:50,106 ♪♪ 601 00:36:51,510 --> 00:37:01,284 ♪ APPARENTLY WE'VE MISSED SOMETHING. 602 00:37:01,286 --> 00:37:04,221 ♪♪ 603 00:37:04,223 --> 00:37:09,459 Narrator: 4 BILLION YEARS FROM NOW, THE MILKY WAY IS NO MORE. 604 00:37:09,461 --> 00:37:12,596 AFTER COLLIDING WITH ANDROMEDA, IT'S REBORN 605 00:37:12,598 --> 00:37:16,499 AS A GIANT ELLIPTICAL GALAXY CALLED MILKOMEDA. 606 00:37:18,437 --> 00:37:22,872 SCIENTISTS THOUGHT GALAXIES THIS BIG WERE DOOMED. 607 00:37:22,874 --> 00:37:25,942 BUT IS HOPE ON THE HORIZON? 608 00:37:28,413 --> 00:37:31,982 THE SLOAN DIGITAL SKY SURVEY HAS SPENT A DECADE 609 00:37:31,984 --> 00:37:36,553 STUDYING OVER A MILLION GALAXIES. 610 00:37:36,555 --> 00:37:40,957 IT'S DISCOVERED A RARE BUT ENORMOUS KIND OF GALAXY -- 611 00:37:40,959 --> 00:37:42,726 A SUPER SPIRAL. 612 00:37:45,631 --> 00:37:48,565 THESE SUPER-SPIRAL GALAXIES ARE SPIRAL GALAXIES 613 00:37:48,567 --> 00:37:50,133 THAT ARE INCREDIBLY SUPER, 614 00:37:50,135 --> 00:37:53,903 AND BY "SUPER," I MEAN THEY HAVE FOUR TIMES THE SIZE, 615 00:37:53,905 --> 00:37:55,605 10 TIMES THE MASS, 616 00:37:55,607 --> 00:37:57,274 AND THEY'RE WEIRD BECAUSE THEY EXCEED 617 00:37:57,276 --> 00:38:00,277 THE SUPPOSED WEIGHT LIMIT FOR SPIRAL GALAXIES. 618 00:38:00,279 --> 00:38:03,280 SO THEY SHOULDN'T HAVE NEW STARS, BUT THEY DO. 619 00:38:03,282 --> 00:38:05,615 THEY'RE VERY HEALTHY GALAXIES. 620 00:38:05,617 --> 00:38:11,221 ♪♪ 621 00:38:11,223 --> 00:38:15,125 Narrator: SCIENTISTS HAVE FOUND JUST 53 SUPER SPIRALS. 622 00:38:18,230 --> 00:38:22,332 SUPER-SPIRAL GALAXIES SHOW THAT IN RARE SITUATIONS, 623 00:38:22,334 --> 00:38:26,903 MASSIVE GALAXIES CONTINUE TO PRODUCE NEW STARS. 624 00:38:30,776 --> 00:38:34,311 SO, IS THIS A LIFELINE FOR MILKOMEDA? 625 00:38:37,149 --> 00:38:39,182 Thaller: WHEN WE THINK ABOUT TWO GALAXIES COLLIDING, 626 00:38:39,184 --> 00:38:40,817 A LOT OF OUR COMPUTER MODELS SUGGEST 627 00:38:40,819 --> 00:38:42,419 THAT THEY REALLY MESS EACH OTHER UP. 628 00:38:42,421 --> 00:38:44,120 THINGS GET VERY CHAOTIC. 629 00:38:44,122 --> 00:38:47,957 BUT OVER TIME, COULD THEY SETTLE BACK DOWN INTO A SPIRAL SHAPE? 630 00:38:47,959 --> 00:38:50,827 AND, IN FACT, THAT MAY BE WHAT HAPPENS WITH SUPER SPIRALS. 631 00:38:50,829 --> 00:38:53,396 ONE OF THE CLUES IS THAT MANY SUPER-SPIRAL GALAXIES 632 00:38:53,398 --> 00:38:54,931 HAVE DOUBLE CORES. 633 00:38:54,933 --> 00:38:57,400 INSTEAD OF THERE JUST BEING ONE SUPERMASSIVE BLACK HOLE, 634 00:38:57,402 --> 00:39:01,237 THERE ARE ACTUALLY TWO ORBITING EACH OTHER. 635 00:39:01,239 --> 00:39:03,840 THE FACT THAT WE SEE SPIRAL GALAXIES WITH TWO CORES 636 00:39:03,842 --> 00:39:05,875 MAKES IT POSSIBLE THAT YOU COULD HAVE A COLLISION 637 00:39:05,877 --> 00:39:08,411 AND STILL SURVIVE AS A SPIRAL GALAXY. 638 00:39:08,413 --> 00:39:11,381 SO MAYBE THERE'S HOPE THAT EVEN THE MILKY WAY WILL BE A SPIRAL 639 00:39:11,383 --> 00:39:13,416 ONCE IT COLLIDES WITH ANDROMEDA. 640 00:39:17,622 --> 00:39:21,424 Narrator: PICTURE THE SCENE -- 6 BILLION YEARS IN THE FUTURE. 641 00:39:23,628 --> 00:39:26,229 MILKOMEDA DRIFTS THROUGH THE UNIVERSE... 642 00:39:28,200 --> 00:39:32,235 ...NOT AS AN ELLIPTICAL GALAXY, BUT AS A SUPER SPIRAL. 643 00:39:34,806 --> 00:39:39,476 THIS SHAPE MEANS THE GALAXY IS FAR MORE STABLE. 644 00:39:39,478 --> 00:39:41,511 THE DAMAGING HEAT AND TURBULENCE 645 00:39:41,513 --> 00:39:45,014 GENERATED BY MILKOMEDA'S SUPERMASSIVE BLACK HOLES 646 00:39:45,016 --> 00:39:51,054 CAN'T DISRUPT STAR-BUILDING GAS WAY OUT IN THE SPIRAL ARMS. 647 00:39:51,056 --> 00:39:56,893 FAR FROM DYING OFF, OUR GALAXY LIVES ON -- 648 00:39:56,895 --> 00:40:00,597 LARGER THAN EVER BEFORE. 649 00:40:00,599 --> 00:40:03,867 BUT THAT ISN'T THE END OF THE STORY. 650 00:40:03,869 --> 00:40:06,970 TENS OF BILLIONS OF YEARS FROM NOW, 651 00:40:06,972 --> 00:40:10,940 COULD THE GALAXY CONTINUE TO GROW? 652 00:40:10,942 --> 00:40:13,176 OUR LOCAL GROUP OF GALAXIES -- 653 00:40:13,178 --> 00:40:15,712 MILKY WAY, ANDROMEDA, TRIANGULUM -- 654 00:40:15,714 --> 00:40:19,449 AND THEN A COLLECTION OF DWARF SATELLITE GALAXIES -- 655 00:40:19,451 --> 00:40:22,519 IS GRAVITATIONALLY BOUND TOGETHER, 656 00:40:22,521 --> 00:40:25,121 AND EVENTUALLY, WE'RE ALL GLUED TOGETHER 657 00:40:25,123 --> 00:40:27,323 INTO A SINGLE MASSIVE OBJECT. 658 00:40:29,060 --> 00:40:30,527 Bullock: WHAT DOES THIS MEAN? 659 00:40:30,529 --> 00:40:32,962 THIS MEANS WE MIGHT BE PART OF ONE OF THE LARGEST STRUCTURES 660 00:40:32,964 --> 00:40:35,165 IN THE UNIVERSE. 661 00:40:35,167 --> 00:40:37,434 Narrator: DURING ITS BILLION YEARS OF LIFE, 662 00:40:37,436 --> 00:40:42,038 THE MILKY WAY CHANGES BEYOND RECOGNITION. 663 00:40:42,040 --> 00:40:45,375 IT SUFFERS COUNTLESS COLLISIONS, 664 00:40:45,377 --> 00:40:49,546 FEASTS ON MANY SMALLER GALAXIES, 665 00:40:49,548 --> 00:40:52,615 AND GIVES BIRTH TO INNUMERABLE STARS. 666 00:40:54,820 --> 00:40:56,886 Thaller: WE TALK ABOUT THE LIFE CYCLE OF GALAXIES -- 667 00:40:56,888 --> 00:41:00,089 HOW THEY'RE BORN, HOW THEY LIVE HEALTHY LIVES MAKING NEW STARS, 668 00:41:00,091 --> 00:41:02,192 AND EVENTUALLY HOW THEY DIE AWAY. 669 00:41:02,194 --> 00:41:04,360 IT'S REALLY NOT AS DEPRESSING AS THAT. 670 00:41:04,362 --> 00:41:06,463 EVERYTHING IN THE UNIVERSE CHANGES. 671 00:41:08,533 --> 00:41:13,837 Narrator: GALAXIES LIKE OURS ARE IN A CONSTANT STATE OF FLUX. 672 00:41:13,839 --> 00:41:16,639 SO WHEN IT COMES TO THE MILKY WAY, 673 00:41:16,641 --> 00:41:19,275 DEATH REALLY ISN'T THE END. 674 00:41:21,179 --> 00:41:22,745 Oluseyi: WHAT WE SEE IN OUR UNIVERSE 675 00:41:22,747 --> 00:41:26,516 IS THAT THERE'S ALWAYS A PROCESS OF BIRTH AND REBIRTH, 676 00:41:26,518 --> 00:41:28,084 SO THE FUTURE OF THE MILKY WAY 677 00:41:28,086 --> 00:41:30,386 IS THAT IT'S GOING TO KEEP ON DOING WHAT IT DOES. 678 00:41:33,024 --> 00:41:34,724 Bullock: GALAXIES ARE EVER-CHANGING. 679 00:41:34,726 --> 00:41:36,159 10 BILLION YEARS AGO, THE MILKY WAY 680 00:41:36,161 --> 00:41:37,994 WAS NOTHING LIKE WHAT IT IS TODAY, 681 00:41:37,996 --> 00:41:39,996 AND CERTAINLY, 10 BILLION YEARS IN THE FUTURE, 682 00:41:39,998 --> 00:41:41,831 IT'LL BE A VERY DIFFERENT PLACE. 683 00:41:44,402 --> 00:41:46,769 Plait: LOOK, I LIVE IN THIS GALAXY. 684 00:41:46,771 --> 00:41:49,372 I HOPE THAT IT CAN FIND A WAY TO REJUVENATE ITSELF 685 00:41:49,374 --> 00:41:51,508 THROUGH COLLISIONS OR SOME OTHER PROCESS 686 00:41:51,510 --> 00:41:53,243 BECAUSE THAT GIVES ME SOME HOPE 687 00:41:53,245 --> 00:41:56,112 THAT IT'LL GO ON FOR A LONG, LONG TIME. 62699

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