(ORDO NEWS) — Four and a half billion years ago, our pale blue dot was born in the debris left after the birth of a star. Since then, we have been in a cosmic dance: the Earth is spinning around the Sun, and the Sun is spinning around the galactic center – the dark, mysterious heart of the Milky Way.
In this dark heart, around which the entire galaxy revolves, is a supermassive black hole called Sagittarius A *, whose mass is about 4.3 million times that of the Sun. We were able to infer her presence and measure it from the movement of objects around her, but we never saw the object itself.
Never, that is, until now.
The image at the top of the screen – looking like a gorgeous blurred orange donut – is the dust around and the shadow of Sgr A* itself, first seen by mankind thanks to the hard work of the Event Horizon Telescope collaboration.
“We were stunned by how well the size of the ring matched the predictions of Einstein’s general theory of relativity,” said EHT project scientist Geoffrey Bower of Sinica Academy in Taipei.
“These unprecedented observations have greatly improved our understanding of what is happening at the very center of our galaxy and provide new insight into how these giant black holes interact with their surroundings.”
The achievement comes three years after the collaboration published the first-ever image of the shadow of a black hole, the supermassive black hole M87*, which has a mass 6.5 billion times that of the Sun, at the center of a galaxy 55 million light-years away. .
Sgr A* is much closer to us, at a distance of about 25,800 light years. But these two black holes represent completely different tasks.
An attempt to depict a black hole is an attempt to depict the invisible. Black holes do not emit any radiation that we could detect. They are so dense that beyond a certain point, known as the event horizon, even light, the fastest thing in the universe, cannot reach the speed of escape from their gravitational pull.
M87* is what we call an active galactic nucleus. This means that it is powered – surrounded by a huge disk of dust and gas that is being pulled into a black hole. Crazy friction and gravity heat up this material so that it glows brightly. This is exactly what we see in the photograph of M87*, where the black hole’s shadow is at the center of the luminous material.
Sagittarius A* may be closer… but he’s not that active. In fact, if Sgr A* were human, it would only consume the equivalent of a grain of rice every million years.
What’s more, the Milky Way’s galactic center is covered in dust that obscures much of what it contains.
Scientists have previously detected a cloud of gas orbiting Sgr A*, the accretion disk of the black hole itself, but it is relatively cold and glows much fainter. Also, because the black hole is smaller, the disk’s orbital period is shorter, which means light changes on very fast time scales.
“Gas in the vicinity of black holes moves at the same speed – almost as fast as light – around Sgr A* and M87*,” says astronomer Chi-Kwan (“CK”) Chan of the University of Arizona.
“But where the gas takes from days to weeks to orbit the large M87*, in the much smaller Sgr A* it orbits in a matter of minutes. This means that the brightness and structure of the gas around Sgr A* changed rapidly during observations EHT collaboration is like trying to get a clear picture of a puppy chasing its tail.”
Inside, something glows brightly in radio waves – it’s Sgr A*, but we’ve never been able to get a detailed picture of it.
To overcome these difficulties, the Event Horizon Telescope brought together eight telescopes from around the world that worked together in an Earth-sized telescope with impressive resolution.
During the observation campaign in 2017, a large number of images were taken, resulting in six terabytes of data. This data had to be processed and analyzed, a process that took years, and new algorithms had to be developed to compensate for the rapid variability.
The images have been grouped into four classes based on similarities, which you can see at the bottom of the image above. Histograms show the relative number of images belonging to each cluster.
Scientists will be chewing on these incredible results for some time to come.
Supermassive black holes are a cosmic mystery. We don’t know how they managed to get so big – Sgr A* is actually quite tiny for one of these behemoths – or how they even formed at the dawn of time.
However, they are the main driving forces behind the evolution of the cosmos. Entire galaxies revolve around them; they drive star formation even beyond their own galaxies.
The supermassive black holes we usually study are active, like M87*. This is because the material in the space around them emits light, and the black hole’s magnetic fields can propel the jets into intergalactic space, which can tell us about the black hole itself.
The calmness of Sgr A* may make it more difficult to portray, but it is this characteristic that makes it an unusual subject to study. Because it doesn’t glow like more active black holes, we’ll be able to see its environment a little more clearly, which in turn will give us a better understanding of the physics of the event horizon.
This could help us understand all sorts of black hole mysteries, such as how accretion occurs, how jets are launched, and even whether general relativity accurately describes the extreme space-time around a black hole.
Surprisingly, the two black holes look very similar. This, the researchers say, means we can draw certain conclusions about black holes.
“We have two very different types of galaxies and two very different black hole masses, but near the edge of these black holes they look surprisingly similar,” says astronomer Sera Markoff of the EHT Science Council at the University of Amsterdam in the Netherlands.
“This tells us that general relativity governs these objects up close, and any differences we see farther away must be due to differences in the material that surrounds black holes.”
The new image opens a new door to the study of these extreme objects. One image of a black hole is amazing. The second means that not only is the first result real, but that we now have a point of comparison to understand how these incredible, extreme objects work.
“Now we can study the differences between these two supermassive black holes to gain valuable new insights into how this important process works,” said astrophysicist Keiichi Asada of Academia Sinica.
“We have images of two black holes – one at the large and one at the small end of supermassive black holes in the universe – so we can go much further in studying how gravity behaves under these extreme conditions than ever before.”
The new results were published in a special issue of The Astrophysical Journal Letters.
You can watch the press conference below and also check out our (now completed) live blog where we covered the announcement in real time.
All times below are in Greenwich Mean Time and in chronological order. Refresh and scroll down the page to see the latest updates. We will add new information every few minutes.
12.40: So, the time has come! We are on the edge of our chairs and immensely happy to share with all of you this grandiose event in astronomy. We will be updating this blog every few minutes, so don’t forget to hit the “Update” button!
12.41pm: For those in the know, here’s what we know so far about the announcement. The results come from the EHT, which gave us the first image of a black hole nearly three years ago.
We also know that the results are for our own Milky Way… which suggests that we may soon see the very first image of the supermassive black hole at the center of our galaxy, Sagittarius A* (Sgr A*).
If astronomers manage to get a direct image of Sgr A*’s event horizon, it will be a historic moment… so make sure you have snacks and plenty of liquid on hand. You won’t want to miss this event.
12.43 pm: It’s not just the fact that this black hole is in our home galaxy that makes this announcement so cool. In fact, this is an incredibly difficult task.
Sgr A* is about 4.3 million times the mass of the Sun, with an event horizon 25.4 million kilometers in diameter, and lies at a distance of 25,800 light-years. Trying to photograph it will be like trying to photograph a tennis ball on the moon.
12.44 pm: Black holes are extremely difficult to draw at the best of times because they are literally invisible, absorbing all electromagnetic radiation. But Sgr A* is even harder to study because it is obscured by a cloud of dust and gas.
Sgr A* was the main target of the EHT observation campaign in April 2017. If astronomers got an image of a black hole’s horizon, then it should look like a glowing doughnut. This is a black hole’s accretion disk, a ring of gas and dust that emits radiation as it orbits Sgr A*.
12.45: 15 minutes left!
12.48 pm: Live broadcast from the headquarters of the European Space Observatory in Germany. But it is broadcast simultaneously with announcements from Washington. Washington DC, Santiago de Chile, Mexico City, Tokyo and Taipei.
We will be listening live:
Thomas Kriechbaum, Max Planck Institute for Radio Astronomy, Germany
Sara Issaun, Center for Astrophysics | Harvard and Smithsonian Institution, USA and Radboud University, Netherlands
José L. Gomez, Andalusian Institute of Astrophysics (CSIC), Spain
Christian Fromm, University of Würzburg, Germany
Mariafelicia de Laurentiis, Federico II University of Naples and National Institute of Nuclear Physics (INFN), Italy.
The National Science Foundation announcement from Washington, D.C. will include:
Kathryn (Kathy) L. Bowman, Associate Professor of Computing and Mathematical Sciences, Electrical Engineering, and Astronomy at Caltech
Vincent Fish, Research Fellow, Haystack Observatory, Massachusetts Institute of Technology
Michael Johnson, astrophysicist at the Center for Astrophysics | Harvard and the Smithsonian
Feryal Ozel, professor of astronomy and physics at the University of Arizona
This may seem like a lot, but there are many more researchers involved in this work. Suffice it to say that it was a huge collaboration.
It is worth noting that all the scientists listed here work with black holes in one way or another.
12.55: Five-minute warning everyone! Last chance to eat!
12.58 pm: I’m not sweating at all here…two minutes left. We have a countdown! We have music! It’s really happening!
13.00: We started.
13.01: THIS IS IT! We’re really going to meet Sgr A*!
02/13: ESO CEO Xavier Barkons briefs us on the developments…
We’ve been this close to Sgr A* many times before, he says: telescopes have studied the movement of stars around the galactic center, which has allowed us to measure the supermassive black hole.
“However, we have not yet seen direct images of this object,” says Barkons. (!!!!)
04/13: Barcons talks about 300+ international scientists, more support staff and eight radio observatories around the world working in collaboration to achieve this groundbreaking result. It’s a timely reminder of what we can achieve when countries work together, he adds.
13.05: Here it is! EHT Project Director Huib van Langeveld with image.
06/13: We fly into the heart of the galaxy to rendezvous with our galactic center, from the plains of Chile, where the ALMA telescope is located.
07/13: LOOK AT THIS!!!
13.08: Wow, this is amazing. To be clear, we can’t see the black hole itself – but it’s there, in this dark spot in the middle of a disk of luminous material.
13.14: Sarah Issaun from Harvard speaks. For the first time, we have direct evidence that Sgr A* is a black hole, she said. The dark spot in the center is the black hole’s shadow; hot gas swirls around it, heated by friction. This gas emits radio emission that we can detect.
Its size is about 52 microarcseconds in the sky, which is equivalent to the image of a donut on the Moon. Since the size of a black hole’s shadow is related to its mass, we can use this to confirm that its mass is about 4 million times that of the Sun. This is exactly what Einstein predicted from general relativity!
Sgr A* looks very similar to the first image of the black hole M87*, although they are very different and in completely different environments. This tells us that, regardless of the size of the medium, the space around the black hole will be dominated by gravity.
13.17: Thomas Kriechbaum of the Max Planck Institute for Radio Astronomy in Germany shares the technical details of this epic achievement. It has taken 25 years to develop and refine methods for combining telescopes around the world into one giant Earth-sized telescope that can achieve the resolution needed to image black holes.
The result was an interferometer that is 3 million times sharper than the human eye. Six terabytes of data were obtained to image Sgr A* – analysis of this data took several years and required the development of new tools.
13.20: José L. Gómez of the Institute of Astrophysics of Andalusia in Spain now goes into more detail about how the eight telescopes of the Event Horizon Telescope work together to make observations.
However, Sgr A* proved to be much more complex than M87*, he says. The region is obscured by dust; and, although the gas around each black hole moves at the same speed, Sgr A* is 1500 times less massive, which means that its gas has a much shorter orbit. This means that the gas was changing on fast time scales during the observations.
13.23: This is the most carefully verified interferometric image ever taken, along with the image of M87*.
HE JUST PROMISED US BLACK HOLES FILMS IN THE FUTURE.
13.25: Christian Fromm from the University of Würzburg in Germany now tells us what the image tells us about Sgr A*.
The team used supercomputers around the world to simulate black holes. When compared to their models, the image tells us that Sgr A* is spinning and that we are facing forward.
13.27: Mariafelicia de Laurentiis of the University of Naples “Federico II” and the National Institute of Nuclear Physics (INFN) in Italy tells us that the size of the shadow of Sgr A* is consistent with relativity, as is that of M87*, despite the fact that these two are black holes accrete materials at completely different rates; Sgr A* is a million times smaller than M87*.
13.29: Studying the environment around a black hole, such as Sgr A* or M87*, will allow us to make new tests of general relativity, hoping to find places where it breaks down, says de Laurentiis. This will help us understand gravity as well as the role that black holes play in our universe.” The best is yet to come!
13.31: This, says Anton Zensus in his closing remarks, is the next level. “We’ve combined the world’s greatest radio telescopes into one Earth-sized chamber.”
The following telescopes participated in the project:
Atakama Large Millimeter/Submillimeter Array (ALMA)
Atacama Pathfinder EXperiment (APEX) in the Atacama Desert in Chile
30m IRAM telescope in Spain
James Clerk Maxwell Telescope (JCMT)
Alfonso Serrano Large Millimeter Telescope (LMT)
Submillimeter Array (SMA)
Arizona Submillimeter Telescope (SMT)
South Pole Telescope (SPT).
Since then, the following have been added to the EHT:
NOrthern Extended Millimeter Array (NOEMA) in France
Greenland Telescope (GLT)
The 12m telescope at Warizon on Kitt’s Peak.
13.35: None of this would have been possible without the 300 scientists who worked on this collaboration. “What about Einstein?” Zensus asks. “I rather think he would be in ecstasy.”
Okay, the press conference is moving to Q&A, so we’ll leave it at that, but stay tuned for our full coverage.
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