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00:00There are 100 billion stars in our galaxy, the Milky Way.
00:11Or maybe there are 200 billion.
00:14Or maybe 400 billion.
00:17No one really knows.
00:21In the universe, there are 100 billion galaxies.
00:24And as technology improves, that number could increase to 200 billion galaxies.
00:30No one is certain.
00:37At the start of the 20th century, there was only one galaxy, our own.
00:49Clearly, over the past 100 years, our knowledge of the universe has expanded.
00:55But there's still a long way to go.
01:00So, what we thought about it was?
01:03See you soon?
01:04It was a challenging time.
01:06The –
01:07The –
01:08The –
01:09The –
01:10It was a –
01:11The –
01:12The –
01:14The –
01:15The –
01:16The –
01:17After more than 40 years, Voyager 1 has left the influence of the solar wind and is heading
01:31for interstellar space. Most of its instruments have been switched off and its nuclear battery
01:37is running low. It will be many thousands of years before it reaches anything other
01:42than interstellar debris. By then, the craft will be long dead. Cosmic distances are so
01:51vast that sending a probe to investigate anything beyond our solar system is not practical.
02:00The only realistic way we have of exploring the universe beyond our neighborhood is by
02:04examining the light that reaches us. The telescope is the main tool we have for
02:12this investigation. And for centuries, astronomers have been building ever larger instruments
02:17to see deeper into the cosmos.
02:22In the 20th century, conventional telescope design reached its limit. Past eight meters
02:27in diameter, the curved primary mirror becomes so heavy that it will sag. As it is aimed at
02:33different targets, its precise curve is distorted by the effects of gravity. In addition, any
02:39extra resolution gained by the larger mirror is not delivered because of atmospheric distortion.
02:49One way to solve both these problems is to put a telescope in space. The Hubble Space Telescope
02:55is the best known example. While the absence of atmospheric distortion was a breakthrough producing
03:01very sharp images, both operational and maintenance costs are considerable. And there are launch constraints
03:07on the size of a telescope that can be delivered to orbit. But engineers have developed a new generation
03:16of Earth-based telescopes with segmented mirrors that overcome the limits to size and can nullify
03:23much of the distortion caused by the atmosphere. The twin Keck telescopes on Mourner Care in Hawaii
03:31were early adopters of this technique. Both have 10-meter mirrors, each in 36 hexagonal segments.
03:40Sensors monitor the mirror's shape and actuators behind each segment continually correct for any
03:46distortions to the curve. The system is called Active Optics. A similar system that works at a more
03:54rapid rate monitors the stability of a bright guide star, or an artificial guide star generated
04:01by a laser. The adaptive optic system reads wave front changes in the atmosphere, then adjusts
04:08the mirror's shape to minimize any distortion.
04:15This image of Jupiter, using adaptive optics, rivals those captured by an orbiting telescope.
04:25Observatories are located at high altitude, where the air is dry and there is no light pollution
04:30from nearby cities. The European Southern Observatory has clusters of telescopes at several sites,
04:38in Chile's Atacama Desert. At Paranal, four identical large telescopes each have 8.2-meter mirrors.
04:47They can combine their light using interferometry. In addition, four auxiliary 1.8-meter telescopes
04:55can link into the cluster. Collectively, they are the Very Large Telescope Interferometer, or VLTI.
05:03Visible light is just a small part of the electromagnetic spectrum. ESO has another facility northeast of Paranal,
05:14on the Chaknantor Plateau. Here, an array of 66 radio dishes observe in millimeter and sub-millimeter
05:22wavelengths. They are linked and also function as an interferometer. Observing in the microwave part of the spectrum
05:32is particularly useful, as these frequencies penetrate gas and dust clouds that remain opaque to higher energy signals.
05:39The more widely the telescopes are separated, the better the angular resolution they can deliver.
05:47This property led radio astronomers around the globe on a unique collaboration.
05:52If radio telescopes around the world could link up, perhaps they could see the unseeable.
06:05General relativity predicted bodies so massive, with such strong gravitation, that not even light could escape from them.
06:13They were called black holes, and at first they were regarded as a mathematical anomaly.
06:20But evidence mounted suggesting that black holes were more than just a theoretical curiosity.
06:26At the center of some galaxies, light far more intense than could be expected from stars has been detected.
06:34Massive bodies such as young stars attract diffuse matter,
06:41which begins swirling and flattens into what's called an accretion disk.
06:45Just as planets orbit stars, it's now accepted that galaxies orbit supermassive black holes.
06:54The very bright light comes from the accretion disk surrounding the black hole.
06:59Matter in the accretion disk is accelerated to incredible speeds, generating intense heat.
07:07Along the axis of rotation, jets of ionized material are ejected at close to the speed of light.
07:17Computer modeling indicated that the vast energy generated by a black hole's interaction with material in the accretion disk could be detected.
07:26The silhouette is the event horizon, the boundary beyond which light cannot escape.
07:33If you want to make a test of the fundamental theories of the universe,
07:39you want to go to the most extreme laboratories in the universe.
07:42And a black hole is that.
07:44Astrophysicists knew that by linking widely separated radio telescopes,
07:49the resolving power of the combined instruments would increase dramatically.
07:53The first attempt at imaging the black hole at the center of our own galaxy was made in 2006,
08:00using instruments in Arizona and Hawaii.
08:03It was not successful, but researchers learned a lot, realizing more telescopes were required.
08:09By 2009, an international collaboration between eight different telescopes had coalesced.
08:18They aimed to capture an image of the supermassive black hole at the center of Messier 87.
08:24So for this experiment it was clear that we need expertise from completely different areas.
08:31And so we needed someone with imaging capabilities,
08:34we needed someone with numerical relativity capabilities,
08:37and in my case we needed someone who can try to find this additional information via pulse source.
08:43And so just being part of this team means you work completely differently.
08:48The project was named the Event Horizon Telescope.
08:53Instruments in North and South America, Europe, Hawaii, and even in Antarctica
08:58would unite to form a telescope with a virtual diameter equal to the Earth.
09:03None of these facilities was designed to work as part of such a large array,
09:09and the technical difficulties facing the team were immense.
09:16Signals from all the sites would have to be processed at a central location,
09:20yet the distances that separated them were so great
09:23that a direct line linking them was impractical.
09:29Data transfer would take place via computer hard drives
09:32that were moved from the place of acquisition to two locations,
09:36the Max Planck Institute in Bonn,
09:39and the MIT Haystack Observatory in Massachusetts.
09:47The Event Horizon Telescope collaboration is a collaboration
09:50of more than 200 scientists with different backgrounds.
09:53They all come from different parts of the world.
09:56They have different experiences, different set of skills.
09:59These are engineers, observers, theoreticians,
10:04and they all work together not only to image the event horizon
10:08of a black hole, but also to understand what we've seen.
10:13Theoreticians already understood that while a black hole
10:16could only ever appear as a silhouette,
10:18its influence upon light emanating from surrounding matter
10:21would be dramatic.
10:24By using mathematical simulation, NASA came up with a moving image
10:28of what they thought the EHT project would reveal.
10:34Viewed from above, the swirling accretion disk appears without distortion.
10:39The smooth inner circle is the photon ring,
10:42light in orbit just outside the event horizon.
10:47When viewed from the side, the black hole's gravitation bends light
10:51from the accretion disk so it can be seen from several angles at the same time.
10:55But no-one really knew what they would see.
11:06For decades, evidence had accumulated that a black hole
11:09at the center of galaxy M87 was consuming huge amounts of material.
11:14Unusually high emissions across the electromagnetic spectrum
11:18were detected in this region,
11:20and images from the Hubble Space Telescope
11:23revealed a huge jet of matter extending out light years.
11:31In April 2017, the EHT was scheduled to make a series of coordinated observations
11:37of the heart of the M87 galaxy.
11:40Each observatory had been equipped with its own atomic clock,
11:46as all data had to be meticulously time-stamped.
11:50Good weather had to happen simultaneously at each site,
11:53and a go-no-go decision was made several hours before each observation.
11:58April 5th, 6th and 7th had good conditions, with data being collected.
12:03Observations were suspended on the 8th and 9th,
12:07due to strong winds at the sites in Mexico and Arizona,
12:10with the final night's observations made on the 10th and 11th of April.
12:19We have this terrible period of waiting where we don't know if it's all worked.
12:23We send all of our data together,
12:25and only when it's truly combined do we know if it's worked.
12:28And then the even harder part begins of analyzing that data
12:33and being very, very careful, doing all the checks and balances
12:37to know that we got it right.
12:39During the observation period, 5 petabytes,
12:43that's 5,000 terabytes, of data was recorded.
12:47The hard drives upon which it was stored weighed half a ton.
12:51They were transported to correlators in Westford, Massachusetts,
12:54and to Bonn in Germany.
12:56While this was relatively simple for most sites,
12:59limited access to the South Pole Telescope delayed its data for several months.
13:07Interpreting radio data as a picture relies upon the black hole's gravitation
13:12bending passing electromagnetic waves.
13:17The EHT will only be able to see the individual points from rays
13:21that are bent toward the Earth.
13:23It is the correlation of all these points that builds them into a recognizable image.
13:28Seeing a black hole actually allows us to not only know they exist,
13:38and not only know an event horizon exists,
13:40it also allows us to test some of the very basic predictions
13:43of the theory of general relativity of Albert Einstein,
13:47which really describes space and time in its completeness.
13:51in its completeness.
13:52And that has never been tested before.
13:54In April 2019, the Event Horizon Telescope team released their image
14:00of the active center of the M87 galaxy.
14:03At its heart was the silhouette of one of the largest black holes we know.
14:10It is roughly 38 billion kilometers across,
14:13the diameter of our solar system.
14:16Its mass is 6.6 billion times greater than our sun.
14:21After predictions flowing from the general theory of relativity more than 100 years ago,
14:28the world finally has proof that black holes do exist.
14:32But this is not the end for the EHT team.
14:35Expanding the number of telescopes in the network will enhance resolution,
14:39and there are plans to investigate the black hole at the center of our own galaxy.
14:49The future of this project is amazing.
14:51We have done something extraordinary.
14:53We have made the first picture of a black hole,
14:56but now we want to do even more.
14:58Now we want to make the first movie.
15:00Now we want to understand how space-time rotates around the black hole.
15:04We will do that by putting more telescopes around the world
15:07to make our virtual lens even better.
15:11Investigation into black holes is not restricted to radio astronomy.
15:16The new technology telescope at La Silla in Chile,
15:19the first instrument equipped with active optics,
15:22began long-term observation of the stars at the center of our own galaxy in 1992.
15:30The NTT observed in the infrared part of the spectrum
15:33because only that light was able to penetrate the heavy clouds
15:36of gas and dust shrouding the central regions of the Milky Way.
15:41A team from the Max Planck Institute plotted the positions of the stars,
15:47building up an image of the way they moved.
15:50They began using the larger telescopes of the European Southern Observatory
15:54at Paranal when they came online.
15:56Over 16 years they mapped the paths of 28 stars.
16:00Well you see the Milky Way center is one of the most important laboratories we have
16:07to study in very great detail what's happening in centers of galaxies,
16:11in much more detail than we can ever hope to do in all other galaxies.
16:15Yet here we are, we can study whether there's a central black hole,
16:19what happens around it and so forth.
16:21All very general issues which you would like to explore
16:23and which you cannot really study that much in detail in other galactic nuclei.
16:30Results showed that the stars are orbiting an invisible point,
16:34which must be our own galaxy's black hole.
16:38Analysis of their highly eccentric paths suggest the Milky Way's black hole
16:43is slightly greater than 4 million times the mass of our Sun.
16:49Of particular interest is the star S2,
16:52which is in a 16-year orbit of the black hole.
16:55Its elliptical path was due to take it to its closest pass,
16:59and its highest speed, in April 2018.
17:03We want to use it as a tool to test whether general relativity,
17:07the theory of Einstein, is actually wrong or right.
17:11General relativity predicts that the black hole's influence
17:15would distort S2's light toward the infrared
17:18as it reached 3% of the speed of light,
17:20which happened, yet another vindication for Einstein.
17:26This test is important to researchers
17:28because general relativity predicts that time stops
17:32inside a black hole's event horizon,
17:34and they want to know if the laws of physics break down
17:37approaching these extremes.
17:39Since Copernicus proposed that the planets orbited the Sun,
17:46astronomers have speculated about planets orbiting other stars.
17:50Advances in telescope technology allowed researchers
17:55to see dips in the brightness of stars
17:57that could only be caused by a transiting planet.
18:00These fluctuations in intensity gave astronomers clues
18:07about the planet's size and its orbit.
18:09A different method monitored the spectral shifts in a star's light
18:15caused by a consistent change in its position,
18:19again only explicable by an orbiting planet.
18:22Using these systems, telescopes around the world began cataloguing exoplanets.
18:32But the methods used were biased toward finding large planets,
18:35similar in size to Jupiter,
18:37that had an easily detectable influence on their star.
18:41And of all the planetary systems out there,
18:45researchers could only use these methods for planetary systems
18:48that were edge-on to the Earth.
18:51Even so, the number of exoplanets we knew about continued to grow.
18:56The worst surprises.
19:01In 2012, a French team discovered an orphan planet
19:05wandering across our galaxy.
19:07It had no star.
19:09It was detected by its emissions in the infrared.
19:16It's difficult to predict the orphan planet's size,
19:19but it's certainly still at the very least several times the mass of Jupiter.
19:23It's difficult to predict the planet's size.
19:25Naturally, researchers were keen to see Earth-sized planets,
19:28planets that could possibly nurture life.
19:31When a new and highly accurate spectrometer called HARPS
19:35was installed at ESO's La Silla 3.5-metre telescope,
19:39this became possible.
19:42Among its discoveries are two planets orbiting Gliese 667c,
19:47about 20 light-years from Earth.
19:50The star is a red dwarf, about one-third the mass of our Sun.
19:56Of particular interest is Gliese 667c,
20:00a planet about five times the mass of the Earth,
20:04and at a distance from its star that puts it in the habitable zone.
20:08Statements about conditions on Gliese 667c have such a large margin of error
20:14that much more work needs to be done before it could be declared
20:18a possible venue for life as we know it.
20:24Another star, 40 light-years away, has a greater range of possibilities.
20:29TRAPPIST-1 is an ultra-cool red dwarf star orbited by seven planets,
20:35all of them close to Earth in size.
20:38To date, this is the largest number of exoplanets detected orbiting an individual star.
20:44At least three of the planets are considered in the habitable zone.
20:52Many different observatories have been gathering data about the TRAPPIST-1 system,
20:57but we still know so little about what kind of environments the different planets might have.
21:02However, the coming generation of telescopes should be able to analyse
21:06the atmospheres of the TRAPPIST-1 planets,
21:09so they will remain a region of close study into the future.
21:18At the moment, around 3,800 exoplanets have been catalogued,
21:23and that number continues to grow.
21:26In 2018, the satellite TESS was launched to search for more exoplanets.
21:31To have a clear view of both the northern and southern skies,
21:40TESS was placed in a 14-day orbit around the Earth
21:43at a 40-degree angle to the plane of the Moon's orbit.
21:47It will systematically map 26 segments of the sky,
21:51recording fluctuations in the brightness of nearby stars that reveal exoplanets.
21:56During its close passes of the Earth,
22:01the Planet Hunter downlinks its data to sites across the United States.
22:06Ground-based observatories will then follow up leads in a more detailed way.
22:11This type of collaboration between orbiting and terrestrial telescopes is becoming common.
22:20An interesting discovery came from the young star, Beta Pictoris.
22:25Fluctuations in its light did not bear the rhythmic signature of an orbiting planet.
22:30Further investigation by the European Southern Observatory revealed three comets orbiting the young star.
22:37Beta Pictoris is only around 20 million years old,
22:42and still displays a protoplanetary ring of dust.
22:45In TESS's first year of operations, at least 29 new exoplanets were confirmed,
22:53with a further 1,000 objects of interest listed in publicly accessible databases.
23:00During its two-year life, TESS will image 200,000 celestial bodies,
23:07including 1,000 of the closest red dwarf stars.
23:11And there will soon be a new planet hunter in orbit.
23:16The Wide Field Infrared Survey Telescope, WFIRST,
23:20will use a different technique known as gravitational microlensing
23:24to detect much smaller exoplanets.
23:30As one star passes in front of another,
23:33its gravitation distorts the distant star's light.
23:37By monitoring the light over time,
23:39a spike in what should be a regular curve
23:42reveals an exoplanet orbiting the lensing star.
23:47But that's not WFIRST's only objective.
23:50There's a gap in knowledge that some cosmologists find embarrassing.
23:56When quantifying the speed at which galaxies rotate,
23:59and the amount of mass they contain,
24:01there's a baffling mismatch.
24:04Our laws of physics say that spinning galaxies
24:07do not contain enough matter,
24:09and therefore enough gravitation,
24:11to prevent them from flying apart.
24:13And yet, they don't.
24:15Astrophysicists came up with the dark matter hypothesis.
24:21This is not just matter that doesn't glow.
24:24It is matter that interacts with nothing else.
24:27The only influence it has is via gravitation.
24:31Halos of dark matter surrounding galaxies
24:34is the current method to explain why they move the way they do.
24:38Estimates say there is five times more dark matter than matter,
24:47yet no one can explain it.
24:52Another fascinating anomaly is that early galaxies,
24:55galaxies whose light has taken more than 10 billion years to reach us,
24:59rotate at a slower rate.
25:01The influence of dark matter is not as pronounced.
25:08New generations of telescope are being built
25:10to help researchers answer some fundamental questions
25:14about the laws governing the universe.
25:16But it seems that cosmology has reached a stage
25:19where it is just discovering how little we know
25:22about what lies beyond the solar system.
25:25the solar system.
25:26.
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