Archive for the ‘black holes’ Category

Physicists detected gravitational waves from four new black-hole mergers

December 3rd, 2018
Artist's rendering of two merging black holes, producing telltale gravitational wave signatures that were picked up by the LIGO/VIRGO detectors..

Enlarge / Artist's rendering of two merging black holes, producing telltale gravitational wave signatures that were picked up by the LIGO/VIRGO detectors.. (credit: Aurore Simonnet/LIGO-Virgo Collaboration/Sonoma State University)

At a weekend workshop in Maryland, physicists from the LIGO and Virgo collaboration reported four previously unannounced detections of gravitational waves from merging black holes, including the biggest-known black-hole collision to date, roughly 5 billion years ago. That merger resulted in a new black hole that is a whopping 80 times larger than the sun.

All four are part of the first official catalog of gravitational wave events (called the Gravitational Wave Transient Catalog, or GWTC-1), listing all events detected to date. Their addition brings the total number to 11. Two scientific papers on the new findings have been posted to the arXiv preprint repository (here and here), pending publication.

LIGO detects gravitational waves via laser interferometry, using high-powered lasers to measure tiny changes in the distance between two objects positioned kilometers apart. (LIGO has detectors in Hanford, Washington, and in Livingston, Louisiana. A third detector in Italy, Advanced VIRGO, came online in 2016.) On September 14, 2015, at 5:51am EST, both detectors picked up signals within milliseconds of each other for the very first time—direct evidence for two black holes spiraling inward toward each other and merging in a massive collision event that sent powerful shockwaves across spacetime.

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Galaxy mergers hide ravenous supermassive black holes

November 14th, 2018
Image of two galaxies merging.

Enlarge / When galaxies collide. (credit: NASA, ESA, the Hubble Heritage Team)

Black holes are… um, black. The point of a black hole is that the force of gravity is strong enough to prevent light from escaping its grasp. But the matter that is being sucked into a black hole is not at all happy about its fate. The matter gets hot and bothered and starts to glow very brightly before it reaches the black hole. This produces what are called luminous accreting black holes.

Most black holes are proud of themselves, sucking down matter right before our very eyes. But others are shy and seem to hide their antisocial behavior, raising questions about whether they were actually there. It turns out that these murderous monsters are hiding behind the gas clouds created by galaxy collisions. It took a serious amount of detective work to penetrate the fog.

Introducing the eyewitnesses

Astronomers have long recognized that not everything in the Universe happens slowly. Sure, our Sun will be stable for billions of years, but when things start to go wrong, they go downhill quickly (use your remaining eight minutes wisely). Likewise, when something big gets sucked into a black hole, it sends a last desperate SOS in the form of a bright X-ray flash.

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Hypothetical black holes could be eating neutron stars

August 10th, 2017

Enlarge (credit: NASA’s Goddard Space Flight Center)

Immediately after the Big Bang, the Universe’s matter was incredibly dense and rippled with random fluctuations. Is it possible that some portions of it reached densities high enough to collapse into black holes?

The idea of primordial black holes has been kicking around in theoretical circles for a while, in part because they could provide much of the dark matter that seems to dominate the Universe’s large-scale structures. But testing for their existence requires some sort of consequence that we could detect, and the theorists have largely come up short there. But now, a team of three physicists writing in Physical Review Letters has come up with a rather intriguing consequence: these black holes could swallow a neutron star that, under the right conditions, would spit out heavy elements.

Truth or consequences

Two things could distinguish primordial black holes from those formed in the collapse of a massive star. One is that they could be nearly any mass, from less than the mass of a star up to thousands of times heavier than anything formed during a supernova. The heavier end of the spectrum is appealing, since it could explain how supermassive black holes appeared so quickly (in astronomical terms) after the Universe’s birth.

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