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.

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.

Did you miss our previous article…
https://mansbrand.com/theres-a-polar-cyclone-on-uranus-north-pole/

Uranus takes 84 years to orbit the Sun, and so that last time that planet’s north polar region was pointed at Earth, radio telescope technology was in its infancy.

But now, scientists have been using radio telescopes like the Very Large Array (VLA) the past few years as Uranus has slowly revealing more and more of its north pole. VLA microwave observations from 2021 and 2022 show a giant cyclone swirling around this region, with a bright, compact spot centered at Uranus’ pole. Data also reveals patterns in temperature, zonal wind speed and trace gas variations consistent with a polar cyclone.

Uranus as seen by NASA’s Voyager 2. Credit: NASA/JPL

Scientists have long known that Uranus’ south pole has a swirling feature. When Voyager 2 flew past Uranus in 1986, it detected high wind speeds there. However, the way the planet was tilted did not allow Voyager to see the north pole.

But the VLA in New Mexico has now been studying Uranus the past several years, and observations collected in 2015, 2021, and 2022 were able to peer deep into Uranus’ atmosphere. The thermal emission data showed that circulating air at the north pole seems to be warmer and drier, which are the hallmarks of a strong cyclone.

“These observations tell us a lot more about the story of Uranus. It’s a much more dynamic world than you might think,” said Alex Akins of NASA’s Jet Propulsion Laboratory in Southern California, who is lead author of a new study published in Geophysical Letters. “It isn’t just a plain blue ball of gas. There’s a lot happening under the hood.”

The researchers said the cyclone on Uranus is similar to the polar cyclones observed by the Cassini mission at Saturn. With the new findings, cyclones (which rotate in the same direction their planet rotates) or anti-cyclones (which rotate in the opposite direction) have now been identified at the poles on every planet in our solar system that has an atmosphere. The researchers said this confirms a broad truth that planets with substantial atmospheres – whether the worlds are made of rock or gas – all show signs of swirling vortexes at the poles.

Uranus’ north pole is now in springtime. As it continues into summer, astronomers hope to see even more changes in its atmosphere.

The post There’s a Polar Cyclone on Uranus’ North Pole appeared first on Universe Today.

Did you miss our previous article…
https://mansbrand.com/juno-reveals-volcanoes-on-io/

Jupiter’s moon Io is the most volcanic world in the Solar System, with over 400 volcanoes. Some of them eject plumes as high as 500 km (300 mi) above the surface. Its surface is almost entirely shaped by all this volcanic activity, with large regions covered by silicates, sulphur, and sulphur dioxide brought up from the moon’s interior. The intense volcanic activity has created over 100 mountains, and some of them are taller than Mt. Everest.

Io is unique in the Solar System, and the Juno orbiter’s JunoCam captured some new images of Io’s abundant volcanic activity.

Io is in a tough position. It’s locked in a kind of gravitational tug-of-war with massive Jupiter and the other Galilean moons, Ganymede, Europe, and Callisto. All that gravitational energy, particularly from Jupiter and Europa, creates friction in the moon’s interior that creates ‘tidal heating.’ That sets it apart from Earth’s volcanism, which is caused largely by the heat from the decay of radioactive isotopes in the mantle, including uranium, potassium, and thorium. In fact, Io produces bout 40% more heat than Earth, an amount that simply cannot be produced by radioactive decay.

This composite image shows how volcanoes dot Io’s surface. It was created with Juno’s JIRAM instrument and its JunoCam instrument. Image Credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM

While Juno’s images of Io are the newest, they’re not necessarily the best. Voyager 1 and Galileo both got closer to Io than Juno did, and their images of the surface are even more stunning.

Galileo captured this image of Io’s surface with a volcano in 1997. Image Credit: NASA/JPL/DLR

But Juno’s much more modern instruments allow it to study Io’s volcanic nature in greater detail. This is important because of some questions scientists would like answers to. Although there’s widespread scientific agreement that tidal heating creates the heat driving all of the moon’s volcanic activity, the heating doesn’t create the volcanoes where we expect them to be, according to our best scientific understanding. One of Juno’s goals is to image the moon’s surface over time to build a more comprehensive picture of the moon’s volcanic activity.

Io has about 115 named mountains, and their average height is about 6,300 m (20,700 ft). Boösaule Montes, at 17,500 metres (57,400 ft) is Io’s tallest moon. Compare that to Mt. Everest’s height of almost 8,850 meters (29,035 ft.) And Io is only 3600 km in diameter, compared to Earth’s 12,700 km diameter. Mountains can be so high on smaller bodies because they have weaker gravity.

Did you miss our previous article…
https://mansbrand.com/erosita-sees-changes-in-the-most-powerful-quasar/