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A star like our Sun only shines the way it does because of its intrinsic balance. Stars are massive, and the inward gravitational pressure from all that mass acts to contain the outward thermal pressure from all the fusion inside the star. They are in equilibrium, or on the main sequence if you like, and the result is a spherical mass of plasma that holds its shape and emits radiation with relative stability for billions of years. Like our Sun.

But eventually, stars teeter over the edge and lose their balance. Stars like our Sun will expand, take on a malevolent red hue, and begin to destroy anything that comes within their grasp.

Like a planet.

As a star like our Sun fuses hydrogen into helium for billions of years, it loses mass. As it loses mass, its inward force of gravity weakens. Eventually, gravity weakens so much that it can no longer counterbalance all the outward pressure from fusion. It cools, turns red, and expands. It becomes a red giant.

Astronomers know all about this because when they look out into the galaxy with powerful telescopes, they can observe and study stars in all stages of life. They also know that our Sun will follow this path. Eventually, it’ll become a red giant and expand. It’ll consume and destroy Mercury, Venus, and most likely Earth too. It’s an inescapable fate. There’s no technological tool we can wield to save Earth.

For us, this is way in the distant future, billions of years from now. Maybe our distant descendants, if we have any, will escape to another planet or moon or crowd into a generational starship and keep humanity going somehow. If that happens, then those humans, if that’s what they still are, will look back ruefully at the wreckage that used to be the inner planets.

That’s a dramatized version of what will happen because, in actual fact, the Sun will slowly heat up well before it expands and becomes a red giant. It’ll boil Earth’s oceans away, shred Earth’s atmosphere, and sterilize the planet. It won’t be cinematic; it’ll happen over a long period of time.

But any way you look at it, a star consuming a planet is a dramatic event. Astronomers at MIT, Harvard, CalTech, and other institutions caught a glimpse of this drama when they saw a distant red giant consuming one of its planets about 12,000 light-years away in the Eagle (Aquila) constellation. Even though red giants aren’t rare, and they’re likely consuming and destroying planets throughout the Milky Way, this is the first time astronomers have spotted it happening.

“We were seeing the end-stage of the swallowing.”

Kishalay De, MIT Kavli Institute

It all started with the Zwicky Transient Facility (ZTF), a wide-angle camera on one of the telescopes at the Palomar Observatory in California. The ZTF is an automated survey facility that images the entire northern sky every two nights. It’s monitored by astronomers who are interested in different types of transients. The ZTF detects transients like supernovae, flare stars, and asteroids in a field called time-domain astronomy, or the study of how astronomical objects change over time.

In May 2020, the ZTF spotted a star that grew brighter by over 100 times in only ten days, then quickly faded again. When something brightens that much, it’s typically a supernova or something similar. But this one was different. After its rapid brightening, there was a colder, longer-lasting signal. According to the team of researchers, only one event can produce this signal: a star devouring a planet.

The researchers presented their findings in a paper titled “An Infrared Transient from a Star Engulfing a Planet” in the journal Nature. The lead author is Kishalay De, a post-doc at MIT’s Kavli Institute for Astrophysics and Space Research.

“We were seeing the end-stage of the swallowing,” De said in a press release announcing the findings.

“It was unlike any stellar outburst I had seen in my life.”

Kishalay De, MIT Kavli Institute

According to the team, this is what they witnessed.

Lead author De was engaged in different research when it happened. He was searching for eruptions in stellar binaries, stars that orbit each other so closely that one draws matter from the other. The matter transfer is variable, and when it happens, the star receiving the matter brightens temporarily. This is one of the types of transients that ZTF is tuned to detect.

Astronomers studying particular types of stellar objects are accustomed to seeing certain patterns in the light the objects emit. The types and amount of light they emit over time give things like stellar binaries tell-tale light curves. The stellar binaries De was studying are called Luminous Red Novae (LRN), but the light signals from the event, now named ZTF SLRN-2020, didn’t match those from any LRN De had seen before.

So when astronomers detect a light curve

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Starship | First Integrated Flight Test | Recap

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Starship gave us quite a show during the first flight test of a fully integrated Starship (S24) and Super Heavy rocket (B7) from Starbase in Texas.

On April 20, 2023 at 8:33 a.m. CT, Starship successfully lifted off from the orbital launch pad for the first time. The vehicle cleared the pad and beach as Starship climbed to an apogee of ~39 km over the Gulf of Mexico – the highest of any Starship to-date.

With a test like this, success comes from what we learn, and we learned a tremendous amount about the vehicle and ground systems today that will help us improve on future flights of Starship.

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ARABSAT BADR-8 Mission Control Audio

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This is the vehicle trajectory and mission control audio without any additional commentary. There may be very long periods of silence. For our full hosted webcast, visit

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https://mansbrand.com/when-black-holes-merge-theyll-ring-like-a-bell/

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When Black Holes Merge, They’ll Ring Like a Bell

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When two black holes collide, they don’t smash into each other the way two stars might. A black hole is an intensely curved region of space that can be described by only its mass, rotation, and electric charge, so two black holes release violent gravitational ripples as merge into a single black hole. The new black hole continues to emit gravitational waves until it settles down into a simple rotating black hole. That settling down period is known as the ring down, and its pattern holds clues to some of the deepest mysteries of gravitational physics.

Gravitational wave observatories such as the Laser Interferometry Gravitational-Wave Observatory (LIGO) have mostly focused on the inspiral period of black hole mergers. This is the period where the two black holes orbit ever closer to each other, creating a rhythmic stream of strong gravitational waves. From this astronomers can determine the mass and rotation of the original black holes, as well as the mass and rotation of the merged black hole. The pattern of gravitational waves we observe is governed by Einstein’s general relativity equations, and by matching observation to theory we learn about black holes.

General relativity describes gravity extremely well. Of all the gravitational tests we’ve done, they all agree with general relativity. But Einstein’s theory doesn’t play well with the other extremely accurate physical theory, quantum mechanics. Because of this, physicists have proposed modifications to general relativity that are more compatible with quantum theory. Under these modified theories, there are subtle differences in the way merged black holes ring down, but observing those differences hasn’t been possible. But a couple of new studies show how we might be able to observe them in the next LIGO run.

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The modified Teukolsky equation. Credit: Li, Dongjun, et al

In the first work, the team focused on what is known as the Teukolsky Equation. First proposed by Saul Teukolsky, the equations are an efficient way of analyzing gravitational waves. The equations only apply to classical general relativity, so the team developed a way to modify the equations for modified general relativity models. Since the solutions to both the Teukolsky and modified Teukolsky equations don’t require a massive supercomputer to solve, the team can compare black hole ring downs in various gravitational models.

The second work looks at how this would be done with LIGO data. Rather than focusing on general differences, this work focuses on what is known as the no-hair theorem. General relativity predicts that no matter how two black holes merge, the final merged black hole must be described by only mass, rotation, and charge. It can’t have any “hair”, or remnant features of the collision. In some modified versions of general relativity, black holes can have certain features, which would violate the no-hair theorem. In this second work, the authors show how this could be used to test general relativity against certain modified theories.

LIGO has just begun its latest observation run, so it will be a while before there is enough data to test. But we may soon have a new observational test of Einstein’s old theory, and we might just prove it isn’t the final theory of gravity after all.

Reference: Li, Dongjun, et al. “Perturbations of spinning black holes beyond General Relativity: Modified Teukolsky equation.” Physical Review X 13.2 (2022): 021029.

Reference: Ma, Sizheng, Ling Sun, and Yanbei Chen. “Black hole spectroscopy by mode cleaning.” Physical Review Letters 130.2 (2023): 141401.

The post When Black Holes Merge, They’ll Ring Like a Bell appeared first on Universe Today.

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