From Science News: “LIGO [and VIRGO] on the lookout for these 8 sources of gravitational waves”

From Science News

May 6, 2019
Lisa Grossman

Astronomers still hope to catch a star going supernova and a bumpy neutron star, among others.

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BANG, CRASH Physicists using the LIGO and Virgo observatories are catching all sorts of cosmic collisions, including of pairs of neutron stars (illustrated). But scientists hope to bag even more exotic quarry. NASA’s Goddard Space Flight Center/CI Lab

Seekers of gravitational waves are on a cosmic scavenger hunt.

Since the Advanced Laser Interferometer Gravitational-wave Observatory turned on in 2015, physicists have caught these ripples in spacetime from several exotic gravitational beasts — and scientists want more.

This week, LIGO and its partner observatory Virgo announced five new possible gravitational wave detections in a single month, making what was once a decades-long goal almost commonplace (SN Online: 5/2/19).

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Picking up

In just one month, scientists have already spotted 5 possible gravitational wave events, plotted here as a function of their approximate distance from Earth. That’s compared to 11 events from all previous observations combined. Most detections are from merging black holes, but neutron star mergers (red) are also in the mix. And one event (yellow) might be a mash up between a black hole and a neutron star.

Gravitational wave detections by LIGO and Virgo are becoming more frequent

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E. Otwell, T. Tibbitts

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“We’re just beginning to see the field of gravitational wave astronomy open,” LIGO spokesperson Patrick Brady from the University of Wisconsin–Milwaukee said May 2 in a news conference. “Opening up a new window on the universe like this will hopefully bring us a whole new perspective on what’s out there.”

The speed and pitch of gravitational wave signals allow astronomers to make out what’s stirring up the waves. Here are the sources of gravitational waves that scientists that already have in their nets, and what they’re still hoping to find.
1. Pairs of colliding black holes

Status: Found

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SWEET SUCCESS For the first time, physicists have directly observed gravitational waves, caused by two black holes colliding (illustrated here). SXS collaboration.

2. Pairs of colliding neutron stars

Status: Found

3. A neutron star crashing into a black hole

Status: Maybe

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TOUGH STUFF An exotic substance thought to exist within a type of collapsed star called a neutron star (illustrated) may be stronger than any other known material.
Casey Reed/Penn State University, Wikimedia Commons

4. A collision involving an intermediate-mass black hole

Status: Not yet

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HIDDEN FIGURE An intermediate-mass black hole about 2,200 times as heavy as the sun may lurk at the center of this dense ball of stars, a globular cluster called 47 Tucanae.
NASA, ESA, Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, J. Mack/STScI, G. Piotto/University of Padua

5. A bumpy neutron star

Status: Not yet

6. Supernova explosions

Status: Not yet

LIGO and Virgo might also be able to pick up gravitational waves from supernova explosions, the bright cataclysms at the end of massive stars’ lives.

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SHINE BRIGHT Supernova 1987A shone as a brilliant point of light near the Tarantula Nebula (pink cloud) in the Large Magellanic Cloud, as pictured from an observatory in Chile.

Supernovas emit many types of light and particles, including ghostly subatomic particles called neutrinos that are born deep in the heart of the explosions (SN: 2/18/17, p. 20). But scientists still don’t know exactly what makes a star explode as a supernova in the first place.

What they do know is that during a supernova explosion, the central core of the star collapses, and the resulting proto-neutron star gathers material from the remainder of the collapsing core. The turbulence at the surface of the proto-neutron star makes it vibrate like a bell, sending off gravitational waves. That specific gravitational wave signal is strongly related to the strength of the turbulence and the structure of the nascent neutron star, astrophysicist David Radice of Princeton University and colleagues report April 29 in the Astrophysical Journal Letters.

7. Waves triggered by the Big Bang

Status: Not yet

8. New sources?

Status: Not yet

LIGO Caltech. LIGO and Virgo detect neutron star smash-ups. May 2, 2019.
See https://sciencesprings.wordpress.com/2019/05/06/from-mit-caltech-advanced-aligo-ligo-and-virgo-detect-neutron-star-smash-ups/

See the full article here .


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