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maria odete madeira
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This Handheld Detector Spotted A Never-Before-Seen Physics Phenomenon https://buff.ly/2wo6UVo
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A New Quantum Understanding is About to Turn Chemistry on Its Head https://buff.ly/2huv1hH
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Neutron star meets black hole. Guess who wins.

A neutron star is not something you'd want to meet up close. About twice the mass of the Sun, compressed to a ball 20 kilometers across, it's made mostly of neutronium, so dense that a cubic centimeter weighs 500 million tonnes. But a neutron star is no match for a black hole!

Sometimes a binary pair of big stars turns into a black hole and a neutron star. Then they will slowly spiral in. Eventually they will collide.

Scientists have been simulating black hole / neutron star collisions, to see what happens next. Sometimes the neutron star falls completely into the black hole, but sometimes, like here, a bunch gets flung out to space.

How much? A lot: up to 1/10 the mass of our Sun! Since neutronium is unstable except at very high pressures, it becomes highly radioactive. The X-rays and gamma rays should be visible from far away.

Francois Foucart, one of the researchers who did these simulations, says:

We are steadily adding more realistic physics to the simulations. But we still don’t know what’s happening inside neutron stars. The complicated physics that we need to model make the simulations very computationally intensive. We are trying to move more toward actually making models of the gravitational-wave signals produced by these mergers.

Those gravitational waves might be seen by LIGO, the Laser Interferometer Gravitational-Wave Observator, which seems to have already spotted a few black hole / black hole collisions.

This particular simulation shows a neutron star spiraling into a black hole that's 3 times as massive. That's pretty light for a black hole. The initial spin of the black hole was chosen to be highly misaligned with the orbital angular momentum of the system: there's an 80 degree angle between them! This makes the orbital plane wobble around crazily.

The neutron star goes through about 2 orbits, during which the separation between the two objects drops from 60 to 30 kilometers. Then tidal forces disrupt the neutron star - in other words, the part close to the black hole feels stronger gravity, so the neutron star gets stretched apart. Most of the neutron star, about 97%, rapidly falls into the black hole. The rest stretches into a long tail, which eventually forms a disk called an accretion disk.

By the end of the simulation, the spin of the black hole and the angular momentum of the disk are misaligned by about 20 degrees. This will make the accretion disk continue to wobble, or precess, over longer timescales.

You can see a more detailed view on a YouTube video made by Robert Garcia:

https://www.youtube.com/watch?v=6g807FFZYqM

and you can see other, newer simulations on Francois Foucart's webpage:

https://sites.google.com/site/francoisfoucart/movies

The quotes are from this article:

http://www.dailygalaxy.com/my_weblog/2017/08/weird-world-of-neutron-stars-astronomers-decode-exotic-states-of-matter-unlike-anything-in-the-unive.html

which was pointed out by +Betsy McCall!

#physics #astronomy
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