This Is Why The Event Horizon Telescope Still Doesn’t Have An Image Of A Black Hole
“Of all the black holes visible from Earth, the largest is at the galactic center: 37 μas.
With a theoretical resolution of 15 μas, the EHT should resolve it.
Despite the incredible news that they’ve detected the black hole’s structure at the galactic center, however, there’s still no direct image.”
Last year, data from the South Pole Telescope, a 10-meter radio telescope located at the South Pole, was added to the Event Horizon Telescope team’s overall set of information. Here we are, though, half a year later, and we still don’t have a direct image of the event horizon for the galactic center’s black hole. There aren’t any problems; the issue is that we have to successfully calibrate and error-correct the data, and that takes time and care to get it right. Science isn’t about getting the answer in the time you have to get it; it’s about getting the right answer in the time it takes to get things right. From that point of view, there’s every reason this is worth waiting for.
The Event Horizon Telescope team is on the right track; here’s where we are right now in our quest to create the first image of a black hole’s event horizon!
The Milky Way Is Hiding Tens Of Thousands Of Black Holes
“This study is of tremendous importance, since it provides us with the first real evidence of what LISA will be looking for, further motivating us to look for these events that, as we now know, must exist. Unlike LIGO’s black holes, these inspiraling events will give us weeks, months, or even years of lead-up time, allowing us to pinpoint exactly where and when we’ll need to look to see these mergers coming. This is the first confirmation of the theory that tens of thousands of black holes ought to exist around supermassive ones at the centers of galaxies, and allows us to better predict how many gravitational wave events we’re likely to see coming from them.“
At the center of our Milky Way, our galaxy houses a supermassive black hole: Sagittarius A*. At four million solar masses, it’s the most massive object in our entire galaxy, while orbiting around it are stars, gas, dust, and many other astrophysical objects. This is a region where new star formation is rampant, and so, in theory, there ought to be many thousands of black holes within just a few light years of Sagittarius A*, some of which ought to be detectable through their emission of X-rays from binary companions. For nearly 20 years, such a detection was elusive, since the flares that occur when black holes absorb large amounts of matter are too rare. But now, using the full suite of archival data from the Chandra X-ray observatory, scientists have found the steady, low-level X-ray emission these systems give off, revealing a population of approximately 10,000 black holes within 3 light years of Sagittarius A*.
The Milky Way is hiding tens of thousands of black holes near the galactic center, and for the first time, we’ve just revealed the surefire signs that they exist.
The Milky Way Is Still Growing, Surprising Scientists
“It’s no big secret that galaxies grow over time. The force of gravity is powerful enough to pull smaller galaxies, gas clouds, and star clusters into larger ones, even over distances of millions of light years. Our own Milky Way has likely devoured hundreds of smaller galaxies over its lifetime, and continues to absorb the dwarf satellites which surround us. But there’s a steadier, more subtle way that galaxies grow: by continuing to form stars from the gas already inside. While most of the stars that form will do so in the plane or central bulge of a spiral galaxy like our own, a new study has shown that galaxies also grow outward over time, meaning that their physical extent increases in space. The implication is that our own galaxy is increasing in size by 500 meters per second: growing by a light year every 600,000 years.”
Imagine a galaxy all by its lonesome out there in the Universe. It’s full of stars, with gas, dust, plasma, and dark matter permeating all throughout it. What’s going to happen to the galaxy over time? You might think that it will continue to form new stars in its spiral arms, while older stars burn out and eventually die. All of that is true, but there’s a subtle but important effect that really adds up over cosmic time: the physical extent of where stars can be found grows as even isolated galaxies age. The Milky Way itself is growing at a rate of 500 m/s, typical of spiral galaxies around this size. It means that by time the Universe is three times as old as it presently is, Milky Way-like galaxies will have grown to be twice as large as they presently are.
While our galaxy itself won’t ever make it to that stage, due to our upcoming merger with Andromeda, many will. Come get the full story here.
This Is How The Milky Way Is Eating Our Galactic Neighbors
“New star formation is triggered by mutual gravitational interactions combined with the Milky Way’s tug.
The gas within these galaxies gets shunted into new clusters, including the local group’s largest star-forming region: 30 Doradus.
But these gravitational interactions also strip the gas away from these dwarfs, where the Milky Way will devour it.
The largest gas stream seems to connect both galaxies, but which cloud it originated from was a mystery.
Until, that is, scientists led by Andrew Fox looked at the absorption effects of this gas from background quasar light.”
While the visible Universe extends for tens of billions of light years, our local group of galaxies extends for only a few million. Around our own Milky Way are a handful of dwarf galaxies, including two bright ones: the Large and Small Magellanic Clouds. These two galaxies contain large numbers of young stars, show evidence of hot, glowing gas, and are destined to be devoured by our Milky Way in cosmically short order. But until that happens, they’re engaged in a cosmic tug-of-war with one another, battling to expel the gas from each other and capture it for themselves. Because the Milky Way is nearby, the expelled gas is getting stretched and drawn into our own galaxy, but which cloud, the Large or the Small, did it arise from?
Owing to new work by a Hubble team led by Andrew Fox, we finally know it’s the Small Magellanic Cloud. Here’s how, and here’s what it means for science.
Einstein’s Ultimate Test: Star S0-2 To Encounter Milky Way’s Supermassive Black Hole
“The largest, closest single mass to Earth is Sagittarius A*, our Milky Way’s supermassive black hole, weighing in at 4,000,000 solar masses.
The star S0-2 makes the closest known approach to this black hole, reaching a minimum distance of just 18 billion kilometers.
That’s only three times the Sun-Pluto distance, or a meager 17 light-hours.”
After a 16 year wait, the closest star to the Milky Way’s supermassive black hole, S0-2, will make its closest approach later this year. At its closest, it should be moving at a whopping 2.5% the speed of light, enabling us to test out Einstein’s relativity in an entirely new regime. We should, for the first time, be able to measure the gravitational redshift from our galactic center, and to track the relativistic “kick” that Einstein’s theory predicts when an orbit gets modified by traveling close to an extremely large mass. New studies have recently shown that S0-2 doesn’t appear to have a binary companion, which makes it even more interesting for such an observation, which won’t come again until the year 2034. As a bonus, scientists hope to shed light on how stars form in the harsh environment of the galactic center at all.
Come find out how the newest test of Einstein could push us past the limits of relativity, or confirm it in an entirely new way!
Milky Way Houses Up To 100 Million Black Holes, With Big Implications For LIGO
“How many black holes are there in the Milky Way? This straightforward question has proven extremely difficult to answer, since black holes are so difficult to directly detect. However, scientists not only have developed indirect methods for locating and even weighing them, we also understand how the Universe forms them: from stars and stellar remnants. If we can understand the different stars that existed at all different times in our galaxy’s history, we should be able to infer exactly how many black holes — and of what mass — exist in our galaxy today. Thanks to a comprehensive study by a trio of researchers from UC Irvine, the first accurate estimates of the number of black holes found in Milky Way-like galaxy have now been made. Not only is our galaxy filled with hundreds of billions of stars, but we also are home to up to 100 million black holes.”
When LIGO announced their first discovery of a black hole-black hole merger, it came as a surprise to almost everyone. The shocking part wasn’t that LIGO had seen merging black holes, but that they were discovered to be so massive. At right around ~30 solar masses each, these were black holes that were much larger than expected, forcing astronomers to confront the fact that they didn’t have a good, comprehensive model for how many black holes – and what mass they should be – were in the Universe. To help this, a trio of researchers from UC Irvine just used the best information we have to simulate galaxy growth and formation, along with stellar evolution, to figure this out. The results they found were that a Milky Way-sized galaxy should have up to 100 million black holes in it, mostly around 10 solar masses each, with a few percent of them being significantly higher in mass. Meanwhile, smaller, lower-mass (and lower-metallicity) galaxies would have fewer black holes that were more massive on average.
This remarkable result gives us our first-ever precise estimate of how many black holes should be in our galaxy, and paves the way for understanding what LIGO (and other gravitational wave observatories) should see in the future!
Are Mass Extinctions Periodic, And Are We Due For One?
“If we start looking at the craters we find on Earth and the geological composition of the sedimentary rock, however, the idea falls apart completely. Of all the impacts that occur on Earth, less than one quarter of them come from objects originating from the Oort cloud. Even worse, of the boundaries between geological timescales (Triassic/Jurassic, Jurassic/Cretaceous, or the Cretaceous/Paleogene boundary), and the geological records that correspond to extinction events, only the event from 65 million years ago shows the characteristic ash-and-dust layer that we associate with a major impact.”
65 million years ago, a catastrophic impact from outer space caused the last great mass extinction on Earth, destroying 30% of the species that lived on our world at the time. These mass extinction events happened many times in Earth’s past, and the Solar System also passes through denser stellar regions of space periodically, as determined by the orbit of the Sun and stars in the Milky Way. It’s a combination of facts that might make you wonder whether the extinction events are also periodic, and if so, whether periodic impacts are predictable. If so, then shouldn’t we be aware of whether we’re living in a time of increased risk, and prepare ourselves for that possibility accordingly? After all, the dinosaurs didn’t have a space program or the capability of deflecting a dangerous object like the one that wiped them out.
But before we go that route, we should take a good look at what the data shows. Are mass extinctions periodic? Are we due? Let’s find out!
How Does Earth Move Through Space? Now We Know, On Every Scale
“Ask a scientist for our cosmic address, and you’ll get quite a mouthful. Here we are, on planet Earth, which spins on its axis and revolves around the Sun, which orbits in an ellipse around the center of the Milky Way, which is being pulled towards Andromeda within our local group, which is being pushed around inside our cosmic supercluster, Laniakea, by galactic groups, clusters, and cosmic voids, which itself lies in the KBC void amidst the large-scale structure of the Universe. After decades of research, science has finally put together the complete picture, and can quantify exactly how fast we’re moving through space, on every scale.”
It’s hard to believe, but despite being at rest here on the surface of Earth, we’re actually hurtling through the Universe in a variety of impressive ways. The Earth spins on its axis, giving someone at the equator a speed of some 1700 km/hr. Yet at even faster speeds, the Earth orbits the Sun, the Sun moves through the Milky Way, and there’s a great cosmic motion that applied to the Milky Way galaxy beyond even that. For a long time, we’ve been able to measure the total effect of all these motions, summed up, by measuring our motion relative to the cosmic microwave background: the leftover glow from the Big Bang. But it’s only very, very recently that we’ve identified the source of all the gravitational causes of this motion. While we’ve known of stars, galaxies, and the large-scale structure of where matter is, it’s new that we’ve quantified the effects of these great cosmic voids.
By combining everything together, we can finally explain the grand total of all of our cosmic motion through the Universe. Come get the full, complete story at last!
We’re Way Below Average! Astronomers Say Milky Way Resides In A Great Cosmic Void
“If there weren’t a large cosmic void that our Milky Way resided in, this tension between different ways of measuring the Hubble expansion rate would pose a big problem. Either there would be a systematic error affecting one of the methods of measuring it, or the Universe’s dark energy properties could be changing with time. But right now, all signs are pointing to a simple cosmic explanation that would resolve it all: we’re simply a bit below average when it comes to density.”
When you think of the Universe on the largest scales, you likely think of galaxies grouped and clustered together in huge, massive collections, separated by enormous cosmic voids. But there’s another kind of cluster-and-void out there: a very large volume of space that has its own galaxies, clusters and voids, but is simply higher or lower in density than average. If our galaxy resided near the center of one such region, we’d measure the expansion rate of the Universe to be higher-or-lower than average when we used nearby techniques. But if we measured the global expansion rate, such as via baryon acoustic oscillations or the fluctuations in the cosmic microwave background, we’d actually arrive at the true, average rate.
We’ve been seeing an important discrepancy for years, and yet the cause might simply be that the Milky Way lives in a large cosmic void. The data supports it, too! Get the story today.
What Will The Death Of The Milky Way Look Like?
“On Earth, we’ve got another billion years or two before the oceans boil and the planet becomes uninhabitable. The Sun will heat up, swell into a red giant, fuse helium in its core, then blow off its outer layers and contract into a white dwarf. But new stars will pop up, too, and shine, and keep the galaxy alive and rife with stars far into the future. But even our own Milky Way will cease to exist: first as we know it, and later on, entirely. When enough time passes, there will be no stars, stellar remnants, or even black holes left at all. This is the cosmic story of the ultimate end of our home in space.”
In the far future, all the galaxies within our Local Group will merge together, with enough gas and stellar material to form trillions upon trillions of new stars. But the amount of fuel is finite, and gravitational interactions are chaotic. At some point, the star forming material contained in our galaxy will come to an end, while more and more stars and stellar remnants are ejected from the galaxy. What will be left, at that point? Just a few stellar corpses orbiting in a halo of dark matter around a central, supermassive black hole. That mass will grow larger and larger, up until a certain point. Once it’s grown all it can, Hawking radiation will result in the decay of that central black hole, unbinding the last structures of normal matter. In the end, there will be nothing left but a large, massive clump of dark matter in the abyss of empty space.
Need something to look forward to? How about the death of the Milky Way, and the return of the Universe to a cold, empty, unstructured state!