by Astronomers have discovered a mystery object in the Milky Way that is more massive than the heaviest neutron star but lighter than the smallest black hole.
The mystery body could help scientists better determine where to draw the dividing line between neutron stars and black holes, both born when a massive star dies.
“Either possibility for the nature of the companion is exciting,” team leader and University of Manchester astrophysics professor Ben Stappers said in a statement. “A pulsar-black hole system will be an important target for testing theories of gravity, and a heavy neutron star will provide new insights into nuclear physics at very high densities.”
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The object was discovered using the MeerKAT Radio Telescope, which consists of 64 antennas located in the Northern Cape of South Africa. The compact interstellar remnant orbits a rapidly spinning neutron star or “millisecond pulsar” located about 40,000 light-years away within a dense cluster of stars known as the “globular cluster” in the Milky Way.
Although a system with two neutron stars would be interesting, if the mystery object is a black hole, this would make the system a popular pulsating black hole-black hole binary radio system. Thanks to the periodic outbursts of the pulsar, which can be used as a timing mechanism, and the intense gravitational influence of the black hole, such a system could be crucial for testing the limits of Einstein’s 1915 theory of gravity, known as general relativity. .
The pulsar, known as PSR J0514-4002E, was spotted through the faint pulses of radio waves it emits as it sweeps past Earth.
As the neutron star rotates at 170 times per second like a cosmic lighthouse, small changes in the very regular pulses allowed researchers to determine that PSR J0514-4002E has an extremely close orbiting object, which which means it can only be a huge remnant. a fallen star.
The team discovered that the pulsar and the mystery object are separated by 5 million miles (8 million kilometers), about 0.05 times the distance between Earth and the sun, and circle each other once every seven Earth day.
The orbiting object has more mass than any known neutron star but less than any known black hole, landing it right in the black hole’s mass gap.
Black holes and neutron stars: See the difference
Neutron stars and black holes are born when massive stars run out of fuel for nuclear fusion and can no longer support themselves against the inward pressure of their own gravity. The star’s core collapses and the outer layers of the dying star are blown away in a supernova explosion.
At the lower end of the mass scale, the collapse of the core star is stopped by the quantum properties of the neutron sea of which it is now composed, and it becomes a neutron star, a stellar remnant with 1 to 2 times its mass. the sun is the width of a city here on Earth, about 12 miles (20 kilometers).
Above a certain mass, however, the quantum pressure that keeps neutrons apart is overcome, and the core collapses completely and becomes a black hole. A neutron star can also exceed this limit and collapse into a black hole if it has a companion star that it can steal material from to increase its own mass.
Astronomers think that if a star’s core still has a mass over 2.2 times the mass of the sun after losing its outer layers and the vast majority of its mass, it is heavy enough to give birth to a black hole.
The problem with this is that the lightest black holes we have seen still have about 5 times the mass of the sun. The absence of black holes between 5 solar masses and 2.2 solar masses is known as the “black hole mass gap”, and casts doubt on the 2.2 solar mass limit for neutron stars.
The black hole mass gap was closed
Using MeerKat to study the globular cluster NGC 1851, located in the southern constellation Columba, Stappers and colleagues discovered the object that may be central to solving this mystery and closing the gap.
The stars in this ancient star cluster are more closely bound than the stars in the rest of the Milky Way. The stars in NGC 1851 are so crowded that they interact with each other, disrupting each other’s orbits and even colliding in extreme cases.
The team thinks that such a collision between two neutron stars could have created the mystery object they detected orbiting the PSR PSR J0514-4002E.
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The team cannot yet identify whether PSR J0514-4002E’s companion is a neutron star, a black hole, or even a previously unknown dense cosmic object, but they know that this system could be is a unique cosmic laboratory for the study of behavior. matter and physics under extreme conditions.
“We are not done with this system yet,” Dutta concluded. “Unveiling the true nature of the companion will be a breakthrough in our understanding of neutron stars, black holes, and whatever else might be lurking in the black hole mass gap.”
The team’s research was published Thursday (January 18) in the journal Science.
