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This celestial body is either the heaviest neutron star or the lightest black hole ever observed.
Astronomy is full of mysterious objects, and an international team of researchers just added another interesting one: a dense compact object that was spotted orbiting a pulsar. This in itself is not that groundbreaking, but the mass of this object is surprising. It is in the so-called mass gap. Researchers observe either the heaviest neutron star or the lightest black hole.
When stars much heavier than the Sun go supernova, they can form two different types of objects. If they are not too big, they will collapse into a neutron star. Neutron stars are stellar objects that consist only of neutrons (particles in the center of an atom with zero electric charge) and are incredibly dense. A teaspoon of neutron star matter weighs as much as a mountain.
Neutron stars can have different properties. Pulsars are a type of neutron star that rotates rapidly around its axis, emitting periodic pulsations. Millisecond pulsars, such as the object in this study (called PSR J0514−4002E), rotate hundreds of times per second. They act as some of the most accurate clocks in the universe.
Another dense object that a supernova can create is a black hole – an object so dense that nothing, not even light, can escape. Observations and theories suggest that the mass of the heaviest neutron star is 2,2 times that of the Sun. The mass of the lightest black hole is expected to be about five times the mass of the Sun. In between there is a mass gap where the object is expected to be a black hole, unless we are missing something in the physics of neutron stars.
The satellite of the pulsar in this case has a mass from 2,09 to 2,71 masses of our Sun. It could be a system with a pulsar and a black hole; or with neutron stars, one of which is pulsating.
“Any opportunity for a companion character is exciting. The pulsar–black hole system will be an important target for testing theories of gravity, and the heavy neutron star will provide new insights into nuclear physics at very high densities,” co-author Professor Ben Steppers from the University of Manchester said in a statement.
The pulsar rotates (and therefore pulsates) 170 times every second, as observed by the MeerKAT radio observatory. By studying tiny variations in this rhythmic signal, the researchers were able to estimate the properties of the system. The precision achieved is incredible, considering that these two celestial bodies are 40 light years apart.
"Think of it as being able to launch a near-perfect stopwatch into orbit around a star nearly 40 light-years away, and then be able to measure the time in those orbits down to the microsecond," added Ewan Barr of the Max Planck Institute for Radio Astronomy , who supervised the study. studying with his colleague Arunima Dutta.
The team believes that the companion is not a direct result of a supernova, but was originally two neutron stars that merged into this massive object.
It may seem strange to have three neutron stars in one system, but this object is in a globular cluster. It is a globular cluster of stars with a much higher density than elsewhere in the galaxy, such as our neighbors. Many stars usually interact in globular clusters. Probably, such interactions led to the formation of an incredible object. And although we still don't know exactly what it is, researchers are trying to find out.
"We're not done with this system yet," Arunima Datta concluded. "Revealing the true nature of the companion is a turning point in our understanding of neutron stars, black holes, and everything else that might be lurking in a black hole's mass rift."
