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Category: cosmology – Page 354

Astronomers find a star dive-bombing our galaxy’s supermassive black hole

At the center of our galaxy lies Sgr A — a supermassive black hole. With over 4 million times the Sun’s mass, you can see why it gets that moniker.

One reason we know its mass is that there’s a cluster of young, luminous stars orbiting around it. These are called S stars, and they form a group around the black hole about a quarter of a light year across — a few trillion kilometers. One of these stars, S2, has an elliptical orbit that takes it to a distance of just 16 billion kilometers from the black hole as it travels on its elliptical orbit. Until recently, that star had the closest encounter we knew of.

Galaxy formation simulated without dark matter

For the first time, researchers from the Universities of Bonn and Strasbourg have simulated the formation of galaxies in a universe without dark matter. To replicate this process on the computer, they have instead modified Newton’s laws of gravity. The galaxies that were created in the computer calculations are similar to those we actually see today. According to the scientists, their assumptions could solve many mysteries of modern cosmology. The results are published in the Astrophysical Journal.

Cosmologists today assume that matter was not distributed entirely evenly after the Big Bang. The denser places attracted more matter from their surroundings due to their stronger gravitational forces. Over the course of several billion years, these accumulations of gas eventually formed the galaxies we see today.

An important ingredient of this theory is the so-called . On the one hand, it is said to be responsible for the initial uneven distribution that led to the agglomeration of the gas clouds. It also explains some puzzling observations. For instance, stars in rotating galaxies often move so fast that they should actually be ejected. It appears that there is an additional source of gravity in the galaxies that prevents this—a kind of “star putty” that cannot be seen with telescopes: dark matter.

We May Finally Have a Way to Detect Hawking Radiation Leaking From Black Holes

O.o!

The epic collision between two neutron stars in 2017 really is the science gift that keeps on giving. As they merged, gravitational waves rippled out across the Universe; now reverberations from that event could confirm a decades-old hypothesis about black holes.

Astronomers poring over the gravitational wave data believe they have found evidence of echoes — something that would only occur in the presence of the ‘quantum fuzz’ produced by Hawking radiation.

“According to Einstein’s theory of general relativity, nothing can escape from the gravity of a black hole once it has passed a point of no return, known as the event horizon,” said astronomer and physicist Niayesh Afshordi of the University of Waterloo in Canada.

Did Scientists Finally Solve the Impossible Physics Riddle?

A theoretical physicist in England has won a prestigious award for her work on the theory of massive gravity, which could explain why gravity hasn’t constrained the rapid expansion of the universe. The $100,000 award honors the work of Claudia de Rham, who has worked for 10 years on a way to turn massive gravity theory into something measurable.

Cosmologists have puzzled for decades about how to marry gravity with the speed at which the universe is expanding. Gravity as we understand it would work to hold the universe together, not let it race apart from itself into eventual oblivion. Enter the counterpart to dark matter, dark energy, which is what scientists call whatever is pulling the universe apart.