00:00This has to be one of the most iconic astronomical images of all times.
00:05In 2019, the world got to see the first ever direct image of a supermassive black hole,
00:12the ring of light surrounding the giant in the galaxy M87.
00:16Now, the Event Horizon Telescope collaboration has released new images of this fascinating object.
00:22Stay tuned, we're in for some surprises.
00:25I'm sure you can't wait for me to show you the new images.
00:32But before I do, let's cover the basics.
00:36Taking an image of a black hole is no mean feat.
00:39Even the largest ones on the sky are so small that it takes a telescope the size of the Earth
00:45to resolve the material swirling in a death spiral around them.
00:49Enter the Event Horizon Telescope, or EHT for short.
00:54The EHT is a network of radio, or rather millimeter, telescopes, including ALMA, spread across the globe.
01:02They're combined to form one giant virtual telescope, using a technique called Very Long Baseline Interferometry.
01:09We did a whole Chasing Starlight episode about the EHT and how it works, so make sure to check that out.
01:15In 2019, the EHT made history with the image of the supermassive black hole at the center of M87, based on data taken in 2017.
01:25The data analysis process was so complicated, it took two whole years.
01:30In 2022, the team published an image of a second black hole, Sag A star, which lies at the center of our own Milky Way galaxy.
01:38But the EHT's work is by no means complete by just taking one image of each of these two black holes.
01:45By observing using different setups and at different epochs, we hope to learn much more about black holes and the physics powering them.
01:53The latest images of the M87 black hole are based on full polarization observations taken in 2017, 2018 and 2021.
02:02And who better to explain them to us than a member of the EHT team itself.
02:07Meet my colleague and friend, Violette Impelizzeri.
02:10Not only did we work at ALMA together for many years, but we also bonded over various activities and adventures.
02:17Violette is an expert on black holes and Very Long Baseline Interferometry.
02:22And she's going to help us understand the new results and why they're so important.
02:27So the first M87 image that was published in 2019 was a true breakthrough result.
02:35It was fundamentally new.
02:37We were showing for the first time the image of supermassive black hole.
02:42Because it was an extraordinary result, it needed to also be repeated.
02:46And we needed to get all the community to believe our result was real, was groundbreaking.
02:52If I had to pick my favorite astronomical result of the last decade,
02:55the M87 image would definitely be in the top three.
02:58But I have to admit that although I was stunned and seriously impressed,
03:02I was also a little bit skeptical.
03:04The image just seemed too good to be true.
03:07I mean, it looked exactly what we expected a black hole to look like.
03:12So I'm really, really happy to see these new results.
03:16In this latest publication, we're showing the results.
03:19We're showing what's come of these three completely independent observations.
03:23And what we find is that basic properties of this image, namely the size of the ring primarily,
03:29do not change for these three different epochs.
03:33The size is very important and actually is the most important characteristic.
03:38The size of the ring depends on two things.
03:40It depends on the mass of the black hole and the distance from us.
03:44Because for M87, we know very accurately from independent observations, previous observations,
03:50the size, the mass of the black hole and the distance from us.
03:53We actually predicted ahead of observing how big we expect the size of the ring to be.
03:59And our observations already in 2019 confirmed our predictions.
04:03So we already claimed back then that Einstein was right.
04:07But it was really important that we repeat this.
04:09And in the EAT and with the new paper and the new observations,
04:12we have shown in 2017, 18 and 2021, the size of the ring as seen by us is the same as constant.
04:20The size of the ring is one thing, but another feature that's striking from the image
04:25is that the lower portion of the ring appears brighter.
04:29This is due to an effect called Doppler boosting or relativistic beaming.
04:35Light from material that is travelling towards us at relativistic speeds
04:39gets boosted in intensity and appears brighter,
04:42while light from material that is travelling away from us appears dimmer.
04:46The exact location of the bright and dark parts depends on the inclination angle
04:51of the system and its disc relative to Earth.
04:54The new images of M87 show that the overall brightness distribution
04:58stays more or less constant over the three epochs,
05:01which is exactly what we would expect.
05:03So the stability of this emission is the same over long periods of time
05:08because it depends on accretion to supermassive black hole.
05:12Because the size of this ring and the position and also the mass of the black hole
05:18stays the same in our human timescales,
05:21we do expect the overall properties to actually remain the same over this period of three years.
05:27So far, so not really unexpected.
05:30But what did the team find that was so surprising?
05:33Let's take a look at one particular aspect of the observations, the polarisation.
05:40You may have heard of polarised sunglasses,
05:43but what do polarisation measurements mean in the context of a black hole?
05:48By measuring the polarisation, we can actually probe these invisible, strong magnetic fields,
05:55these superhighways.
05:56They're so strong that they actually carry the plasma around.
06:00So the magnetic fields are extremely important.
06:04So it's very important that we also understand what they look like and what they're strengthened.
06:08This is why it's so critical that we study the polarisation
06:11and the changes in the polarisation year to year.
06:14OK, so the polarisation tells us about the shape of the magnetic field,
06:19which determines how matter moves close to the black hole.
06:23If we take a look at the images taken at different epochs,
06:28we see that the polarisation changes dramatically.
06:31In 2017, the magnetic fields spiral one way.
06:35In 2018, they've all but disappeared.
06:38And by 2021, they're going in the other direction.
06:42A surprise, according to Violette.
06:44The magnitude of these changes was actually unexpected.
06:48In fact, the second epoch, the magnetic fields, i.e. the polarisation,
06:52the polarisation is extremely faint.
06:54And we do not fully understand why that is happening.
06:57We have some ideas, we have some clues, but we don't fully understand what's happening there.
07:01So it's very intriguing, it's very exciting.
07:04One of the main limitations of the EHT is the relatively small number of individual stations
07:09making up this giant virtual telescope.
07:12If you imagine the EHT as a huge block of Swiss cheese, you'd end up with more whole than actual cheesy goodness.
07:20This makes reconstructing the image of a black hole via interferometry extremely challenging
07:26and creates gaps in the data at certain spatial scales.
07:30Placing individual telescopes very far away from each other allows us to resolve very small spatial scales,
07:37such as the accretion ring around M87.
07:40While putting the telescopes close to each other allows us to uncover larger structures,
07:45such as the giant jet emanating from the black hole in M87.
07:49So one of the most obvious ways of improving the EHT is to add more antennas at different distances from each other to the network.
07:58For the last observations, the 2021, for example, we had two extra telescopes, a Kitt Peak and NOIMA.
08:05And already with these observations, we could see that they make a big difference.
08:09Because they are what we call intermediate baselines, they allowed us to see some of the extended gas
08:15that is not just the ring itself, but it's the part that connects the ring with the really, really large jet that goes far out.
08:22And bridging these two regions has been extremely challenging because these are really intermediate sizes.
08:28So one of the major outcomes actually of this paper is that we can see starting to see this intermediate gas.
08:38The publication of the first ever direct image of a black hole was not just the culmination of decades of effort,
08:44of decades of efforts and a huge accomplishment, but also the start of a whole new era of black hole research.
08:51Thanks to the ongoing efforts, not only of the EHT team, but also staff at the associated observatories and research teams worldwide,
09:00we were able to check once again and confirm the predictions of Einstein's general relativity
09:06and challenge our understanding of magnetic fields in these extreme black hole environments.
09:13On the off chance that some of you think black holes are boring, well, Violette has the last word.
09:20They're really exciting and they change over time and it's worth observing them for the long run.
09:25They tell us how they accrete, how they spew matter out, and we have still a lot to learn.
09:30There's a lot more coming, besides our frequencies, we're planning to have movies,
09:34we're planning to have more antennas, maybe send antennas into space.
09:37So the EHT is really, you know, it's a long path to go, a lot more to discover.
09:43I know a lot to find out and discover.
09:44So I should love to find out more about the novel.
09:45That we have almost gone.
09:46We'll see you next time and see.
09:48Well that knowledge is probably 2x.
09:49Thank you so much for talking about this novel.
09:50There was some book is Pro Broker and a bunch of books.
09:51It's a myth of Book From Eastern 950-iges Magic
09:56people in another episode.
10:02Then things are going to be a little so you'll find a mechanic.
10:03I need to save the 950 gauge locked open, and we'll find a logo that I've read in more
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