Category: black hole

Astronomers Find A ‘Cloaked’ Black…

Astronomers Find A ‘Cloaked’ Black Hole 500 Million Years Before Any Other

“The first stars should lead to modest black holes: hundreds or thousands of solar masses. But when we see the Universe’s first black holes, they’re already ~1 billion solar masses. The leading idea is black holes form and merge, and then rapidly accrete matter at maximal rates. But those rapidly growing black holes should be invisible, obscured by the dense gas clouds they feed upon. They were, until now. New observations have revealed the earliest “cloaked” black hole ever.”

How do black holes get so big so quickly in this Universe? It’s one of the great mysteries in astrophysics, but the hope has been that better observations of the first billion years of the Universe will help solve this puzzle. If the seeds of black holes can gather enough gas around them to feed on, they just might get there. But the difficultly then comes in locating and finding these obscured, “cloaked” black holes. While they’ve been found relatively nearby, telling us that such a phenomenon does occur, they’ve never been found at very early times: within the first billion years of the Universe.

Well, with new Chandra X-ray observations, all of that has changed. We found a cloaked black hole just 850 million years after the Big Bang. It might be the key to solving this cosmic puzzle at long last.

This Is Why Black Holes Must Spin At Almost …

This Is Why Black Holes Must Spin At Almost The Speed Of Light

“Realistically, we can’t measure the frame-dragging of space itself. But we can measure the frame-dragging effects on matter that exist within that space, and for black holes, that means looking at the accretion disks and accretion flows around these black holes. Perhaps paradoxically, the smallest mass black holes, which have the smallest event horizons, actually have the largest amounts of spatial curvature near their horizons.

You might think, therefore, that they’d make the best laboratories for testing these frame dragging effects. But nature surprised us on that front: a supermassive black hole at the center of galaxy NGC 1365 has had the radiation emitted from the volume outside of it detected and measured, revealing its speed. Even at these large distances, the material spins at 84% the speed of light. If you insist that angular momentum be conserved, it couldn’t have turned out any other way.”

Have you ever wondered how black holes, ranging from a few times our Sun’s mass up to billions of times as massive, can spin so rapidly? Most black holes, as far as we can tell, are spinning very close to the speed of light: the ultimate speed limit of the Universe. Yet most stars, like our Sun, rotate extremely slowly: just once over a period of many days (or even longer).

So how does a slowly-rotating star, which goes supernova and forms a black hole, give rise to an object spinning near the cosmic speed limit? Find out today.

General Relativity Rules: Einstein Victorious …

General Relativity Rules: Einstein Victorious In Unprecedented Gravitational Redshift Test

“The most interesting part of this result is that it clearly demonstrates the purely General Relativistic effect of gravitational redshift. The observations of S0-2 showcase an exact agreement with Einstein’s predictions, within the measurement uncertainties. When Einstein first conceived of General Relativity, he did so conceptually: with the idea that acceleration and gravitation were indistinguishable to an observer.

With the validation of Einstein’s predictions for the orbit of this star around the galactic center’s black hole, scientists have affirmed the equivalence principle, thereby ruling out or constraining alternative theories of gravity that violate this cornerstone of Einsteinian gravity. Gravitational redshifts have never been measured in environments where gravity is this strong, marking another first and another victory for Einstein. Even in the strongest environment ever probed, the predictions of General Relativity have yet to lead us astray.”

If you want to test Einstein’s General Relativity, you’ll want to look for an effect that it predicts that’s unique, and you’ll want to look for it in the strongest-field regime possible. Well, there’s a black hole at the center of our galaxy with 4 million times the mass of the Sun, and there’s a star (S0-2) that passes closer to it, during closest approach, than any other. In May of 2018, it made this closest approach, coming within 18 billion km (about twice the diameter of Neptune’s orbit) of the black hole, and zipping around at 2.7% the speed of light.

Did Einstein’s predictions for gravitational redshift come out right? You bet they did: 5-sigma, baby! Come get the full, amazing story here!

Ask Ethan: What’s It Like When You Fall …

Ask Ethan: What’s It Like When You Fall Into A Black Hole?

“[W]hat is it like to be/fall inside a rotating black hole? This is not observable, but calculable… I have talked with various people who have done these calculations, but I am getting old and keep forgetting things.”

I get a lot of questions that people submit for Ask Ethan, but only rarely do they come to me from other scientists who tower above me in the field. This week’s question, from Event Horizon Telescope scientist extraordinaire Heino Falcke, asks me to help him visualize what it would look like if you fell into a black hole. Not just any black hole, mind you, but a realistic, rotating black hole. There’s really only one person on Earth who understands this well enough: Andrew Hamilton, who has devoted the last 15 years of his life to figuring out what it looks like and what it means when this actually happens.

So what did I do? I went and met Andrew, interviewed him, read his papers, and used his simulations to give everyone the best answer I could. I hope you love it, and I hope (even moreso) that I got it right!

Ask Ethan: How Does The Event Horizon Telescop…

Ask Ethan: How Does The Event Horizon Telescope Act Like One Giant Mirror?

“I’m having difficulty understanding why the EHT array is considered as ONE telescope (which has the diameter of the earth).
When you consider the EHT as ONE radio telescope, I do understand that the angular resolution is very high due to the wavelength of the incoming signal and earth’s diameter. I also understand that time syncing is critical.
But it would help very much to explain why the diameter of the EHT is considered as ONE telescope, considering there are about 10 individual telescopes in the array.”

Humanity has imaged a black hole’s event horizon! It’s been less than a month since the news was announced, and it’s still hard to get over what a phenomenal achievement it was. It’s very difficult to conceive of how, though, we can treat 8 different telescopes and telescope arrays, all stitched together, as acting like a single giant mirror. But that’s exactly what the Event Horizon Telescope did. In fact, that’s what it needed to do, or it would never have been able to achieve the resolutions necessary to construct the first image of a black hole’s event horizon.

But we have it! We achieved it! And here’s the conceptual way you can understand it, even if you barely understand the way a single telescope works.

Ask Ethan: How Can A Black Hole’s Singul…

Ask Ethan: How Can A Black Hole’s Singularity Spin?

“How [is] angular momentum conserved when stars collapse to black holes? What [does] it means for a black hole to spin? What is actually spinning? How can a singularity spin? Is there a “speed limit” to this spin rate and how does the spin affect the size of the event horizon and the area immediately around it?”

When you think about a black hole, you probably think about an enormous amount of mass confined within an event horizon, collapsing down to a singular point at its center. And this is fine: this is just how Karl Schwarzschild conceived of it way back in 1916. But the stars and other forms of matter that potentially give rise to black holes cannot be point-like, since they all rotate. What happens to those rotational properties, or to angular momentum (which is always conserved), when they form a black hole? There are a lot of counterintuitive things that occur inside, and you’ll want to learn them all after reading this! 

In the aftermath of the Event Horizon Telescope’s big reveal, you just might join me in hoping Roy Kerr wins the Nobel Prize for his incredible 1963 paper.

Ask Ethan: How Can A Black Hole’s Singul…

Ask Ethan: How Can A Black Hole’s Singularity Spin?

“How [is] angular momentum conserved when stars collapse to black holes? What [does] it means for a black hole to spin? What is actually spinning? How can a singularity spin? Is there a “speed limit” to this spin rate and how does the spin affect the size of the event horizon and the area immediately around it?”

When you think about a black hole, you probably think about an enormous amount of mass confined within an event horizon, collapsing down to a singular point at its center. And this is fine: this is just how Karl Schwarzschild conceived of it way back in 1916. But the stars and other forms of matter that potentially give rise to black holes cannot be point-like, since they all rotate. What happens to those rotational properties, or to angular momentum (which is always conserved), when they form a black hole? There are a lot of counterintuitive things that occur inside, and you’ll want to learn them all after reading this! 

In the aftermath of the Event Horizon Telescope’s big reveal, you just might join me in hoping Roy Kerr wins the Nobel Prize for his incredible 1963 paper.

Ask Ethan: How Does Very-Long-Baseline Interfe…

Ask Ethan: How Does Very-Long-Baseline Interferometry Allow Us To Image A Black Hole?

“[The Event Horizon Telescope] uses VLBI. So what is interferometry and how was it employed by [the Event Horizon Telescope]? Seems like it was a key ingredient in producing the image of M87 but I have no idea how or why. Care to elucidate?”

If it were easy to network radio telescopes together across the world, we’d have produced an image of a black hole’s event horizon long ago. Well, it’s not easy at all, but it is at least possible! The technique that enabled it is known as VLBI: very-long-baseline interferometry. But there are some critical steps that aren’t very obvious that need to happen in order for this method to succeed. Remarkably, we learned how to do it and have successfully employed it, and the Event Horizon Telescope marks the first time we’ve ever been able to get an image with a telescope that’s effectively the size of planet Earth!

Come get the incredible science behind how the technique of VLBI enabled the Event Horizon Telescope to construct the first-ever image of a black hole’s event horizon!

Ask Ethan: How Does Very-Long-Baseline Interfe…

Ask Ethan: How Does Very-Long-Baseline Interferometry Allow Us To Image A Black Hole?

“[The Event Horizon Telescope] uses VLBI. So what is interferometry and how was it employed by [the Event Horizon Telescope]? Seems like it was a key ingredient in producing the image of M87 but I have no idea how or why. Care to elucidate?”

If it were easy to network radio telescopes together across the world, we’d have produced an image of a black hole’s event horizon long ago. Well, it’s not easy at all, but it is at least possible! The technique that enabled it is known as VLBI: very-long-baseline interferometry. But there are some critical steps that aren’t very obvious that need to happen in order for this method to succeed. Remarkably, we learned how to do it and have successfully employed it, and the Event Horizon Telescope marks the first time we’ve ever been able to get an image with a telescope that’s effectively the size of planet Earth!

Come get the incredible science behind how the technique of VLBI enabled the Event Horizon Telescope to construct the first-ever image of a black hole’s event horizon!

For those who want more precise information ab…

https://iopscience.iop.org/article/10.3847/2041-8213/ab0ec7

https://iopscience.iop.org/article/10.3847/2041-8213/ab0c96

https://iopscience.iop.org/article/10.3847/2041-8213/ab0c57

https://iopscience.iop.org/article/10.3847/2041-8213/ab0e85/meta

https://iopscience.iop.org/article/10.3847/2041-8213/ab0f43/meta

https://iopscience.iop.org/article/10.3847/2041-8213/ab1141/meta