Astrophysics

Astrophysics / cosmology / Physics / etc.

Dark Energy, Numerical Relativity, and Astrophysics

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binary neutron star merger

So I did an interview for the “Tilting at the Universe” podcast. In it, I describe: the history of dark energy and the expanding universe, how the mystery of dark energy may be solved once we reconcile quantum mechanics and general relativity, how the astrophysics of black holes and neutron stars may help us understand quantum gravity, and how my field of numerical relativity fits in to all of this. I think I did a pretty good job of explaining what excites me about the field. So check it out. The interview is here. In the interview, I mention

Astrophysics / Physics / Relativity / etc.

The Black Holes that Created LIGO’s Gravitational Waves

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LIGO merger Bohn

A little over a week ago, the LIGO collaboration detected gravitational waves emitted during the in-spiral and merger of two black holes. And the world’s scientists, myself included, collectively went bananas. Last week, I attempted to summarize the event and capture some of the science, and poetry, that has us so excited. In short, gravitational waves provide us a totally new way to look at the universe. LIGO’s one detection has already provided us with a wealth of information about gravity and astrophysics. Today, I summarize some of what we’ve learned. Black Holes As We Knew Them In the

Astrophysics / Physics / Relativity / etc.

The Poetry of LIGO’s Gravitational Waves

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Binary Black Hole Merger Signal

Yesterday the LIGO scientific collaboration announced that they had detected the gravitational waves from the in-spiral and merger of two black holes, shown in figure 1. It would not be an overstatement to say that this result has changed science forever. As a gravitational physicist, it is hard for me to put into words how scientifically important and emotionally powerful this moment is for me and for everyone in my field. But I’m going to try. This is my attempt to capture some of the science—and the poetry—of LIGO’s gravitational wave announcement. The Source About 1.3 billion years ago

Astrophysics / Physics / Relativity / etc.

The Geodetic Effect: Measuring the Curvature of Spacetime

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gravity probe B in curved spacetime

A couple of weeks ago, I described the so-called “classical tests of general relativity,” which were tests of early predictions of the theory. This week, I want to tell you about a much more modern, difficult, and convincing test: A direct measurement of the curvature of spacetime. It’s called the geodetic effect. This is the eighth post in my howgrworks series. Let’s get to it. We know from general relativity that gravity is a distortion of how we measure distance and duration. And that we can interpret this distortion as the curvature of a unified spacetime. When particles travel

Astrophysics / Physics / Science And Math

Type 1a: The Other Type of Supernova

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Supernova 1994D

When people hear “supernova” they usually think of a star that runs out of fuel. Without the engine of nuclear fusion to heat it, the star collapses under its own weight, which triggers a huge explosion. This is a “core-collapse supernova,” one of the most energetic events in the universe. The result is usually a neutron star or a black hole. However, there’s another type of supernova, one in which a star whose nuclear fires long ago petered out is reignited, causing a catastrophic explosion. This is the type Ia supernova. We start our story with the type of

Astrophysics / Geometry / Mathematics / etc.

Speculative Sunday: Can a Black Hole Explode?

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Cassiopeia A Spitzer Image

Nothing can escape the gravitational pull of a black hole, not even light. That’s why they’re, well, black. (Of course, as I’ve described before, black holes can glow very brightly, thanks to all the in-falling matter. Sometimes they even produce gamma rays. I’m also ignoring the negligible amount of Hawking radiation that black holes theoretically produce.) Once you pass the event horizon of a black hole, you cannot ever escape. Escape is simply forbidden by the laws of physics. That is, of course…if there actually is an event horizon, not just something that looks like one. Carlo Rovelli ,

Astrophysics / Physics / Relativity

The Curvature of Spacetime

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Abell 2218

Spacetime is curved. We’ve all heard the line. But what does it mean? Well on the largest scales, the curvature of spacetime is abundantly clear as the warped fabric of the universe distorts images of distant objects. The image below is of the Abell 2218 galaxy cluster, taken by the Hubble Space Telescope. The cluster is very massive so it warps the spacetime around it. This warped spacetime acts as a lens so that light light coming from galaxies behind Abell 2218 is spread out much more than it should be. The result is that images of galaxies behind

Astrophysics / Physics / Relativity / etc.

Simulating Gamma Ray Bursts

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It was the mid 1960s. The United States and the Soviet Union had recently signed the Partial Nuclear Test Ban Treaty, which forbid the detonation of nuclear weapons except underground. Since neither nation trusted the other, each was carefully monitoring the other for non-compliance. In particular, the United States feared that the soviets might be, I kid you not, testing bombs behind the moon. Vela The United States solved this problem with the Vela satellites. When a nuclear bomb goes off, it emits a short burst of gamma rays, which are rays of extremely high energy light. The Vela

Astrophysics / Physics / Science And Math

The Long Arms of the Black Hole

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Black holes are incredibly messy eaters. As matter falls into a spinning black hole, that matter can be accelerated to incredible velocities and launched out the poles. In the case of the supermassive black holes at the centers of galaxies, these are the most energetic events in the universe since the Big Bang. The exact mechanism for the creation of these jets is unknown. There are two competing theories, one called the Blandford-Payne mechanism, and one called the Blandford-Znajek mechanism. The details are too fiddly to get into here, but the former has more to do with the in-falling

Astrophysics / cosmology / Physics / etc.

The Universe Is an Inside-Out Star

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the CMB on our sky

No, not really. But as we’ll see, it’s a useful analogy. Today we’ll learn about sound waves in the sun and how, if we imagine that the universe is the sun but inside-out, these are the same as the sound waves that filled the early universe. DISCLAIMER: This is a pedagogical exercise only! I am not claiming the universe is ACTUALLY an inside-out star or that scientists think of it as one. Sound Waves in the Sun I’m sure you won’t be surprised when I say that the sun is a complicated beast. A nuclear furnace burning at tens