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Gravitational wave astronomers discover mysterious objects in mass gap



Black hole neutron star

The black hole depicted by the artist is about to devour the neutron star. Image source: Carl Knox of OzGrav ARC Center of Excellence

For decades, astronomers have been confused about the gap between neutron stars and black holes, but a major new discovery has discovered a mysterious object in the so-called “mass gap”.

Gravitational wave group University of PortsmouthThe Institute of Universe and Gravity played a key role in this research, which will change the way scientists view neutron stars and black holes.

When the most massive stars die, they collapse under their own gravity and leave black holes. When stars with a smaller mass die, they will explode in supernovas, leaving behind dense, dead-point stellar wrecks called neutron stars.

Whenever an asymmetric object accelerates, it emits gravitational waves, one of the strongest detectable sources Gravitational wave From the collision of neutron stars and black holes. Both of these objects were created at the end of the life of huge stars.

“These discoveries are so exciting because we have never detected an object with a mass completely within the theoretical mass gap between the neutron star and the black hole.”- Dr. Laura Nuttall, an astrophysicist at the University of Portsmouth

Heaviest Neutron star No more than two and a half times our solar mass or 2.5 solar masses, and is the lightest Black hole There are about five solar masses.

The National Science Foundation Laser Interferometer Gravity Wave Observatory (Ligao) And the European Virgo probe announced the discovery of 2.6 solar mass objects and placed them firmly in the mass gap.

LIGO consists of two gravity wave detectors, 3,000 kilometers apart in the United States, one in Livingston, Louisiana, and one in Hanford, Washington. The Virgo detector is located in Casina, Italy.

Dr. Laura Nuttall, a gravitational wave expert at the University’s Institute of Universe and Gravity, said: “These findings are so exciting because we have never detected that the mass lies entirely within the theoretical mass gap between neutrons The object inside. Before the stars and black holes. Is it the lightest black hole we have ever seen or the heaviest neutron star?”

Portsmouth (Portsmouth) doctoral student Connor McIsaac conducted an analysis that calculated the importance of this event.

Dr. Nuttall added: “Connor’s analysis convinced us that this is a real astrophysics phenomenon, not some strange tool behavior.”

The object was discovered on August 14, 2019, and merged with 23 solar-mass black holes, producing a splash of gravitational waves found on Earth by LIGO and Virgo.

The cosmic merger described in this study, the GW190814 event, resulted in the final black hole, about 25 times the mass of the sun (some of the combined mass was converted into an energy explosion in the form of gravitational waves). The newly formed black hole is about 800 million light years away from the earth.

Before the two objects merged, their mass differed by 9 times, making it the most extreme mass ratio known in the event of gravitational waves. Another recent LIGO-Virgo event is called GW190412, which occurred between two black holes with a mass ratio of 3:1.

“I think Pac-Man will eat a little bit, and when the agglomerates are highly asymmetric, they can eat smaller neutron stars in one bite.” Vicky Kalogera, Northwest University,United States

Northwestern University professor Vicky Kalogera said: “For the current theoretical model, it is a challenge to form such a large mass ratio of compact objects, and low-quality partners are located in the mass gap. This discovery means that these events The frequency of occurrence is much higher than we expected, which makes it a truly attractive low-quality object.

“This mysterious object may be a neutron star merged with a black hole, which is an exciting possibility theoretically expected, but has not yet been confirmed by observation. However, its mass is 2.6 times the mass of our sun, more than the modern pair of neutron stars The highest quality prediction, it may be the lightest black hole ever.”

When LIGO and Virgo scientists discovered this merger, they immediately alerted the astronomy community. Dozens of ground-based and space-based telescopes were tracked to search for light waves generated during the event, but none received any signals. So far, in the event called GW170817, only this light corresponding to the gravity wave signal can be seen. The event was discovered by the LIGO-Virgo network in August 2017 and involved a violent collision between two neutron stars, which was subsequently witnessed by dozens of telescopes on Earth and in space. The collision of neutron stars is a mess. The matter is thrown out in all directions, so it is expected to glow. On the contrary, in most cases, people think that black hole merger will not bring light.

According to LIGO and Virgo scientists, for some possible reason, the light-based telescope did not see the August 2019 event. First, this event is six times away from the 2017 merger transaction, so it is more difficult to pick up any optical signals. Second, if the collision involves two black holes, there may not be any light. Third, if the object is actually a neutron star, it may be engulfed by its mass 9 times that of the black hole’s partner. A neutron star completely consumed by a black hole will not emit any light.

“I think Pac-Man will eat a little bit,” Kalogera said. “When the mass is highly asymmetric, the smaller neutron star can be eaten in one bite.”
Future observations using LIGO, Virgo, and possibly other telescopes may capture similar events, which will help reveal whether the mysterious object is a neutron star or a black hole, or whether there are other objects in the mass gap.

Papers on detection have been accepted for publication in the Astrophysical Journal Letters.

More information about this study:

Reference: R. Abbott et al., “GW190814: Merged gravitational waves of 23 solar mass black holes and 2.6 solar mass dense objects”. Wait, June 23, 2020, Astrophysical Journal Letter.
DOI: 10.3847 / 2041-8213 / ab960f




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