A new and unknown object in the Milky Way that is heavier than the heaviest neutron stars known to scientists, and yet lighter than the lightest known black holes, has been discovered by astronomers.
Researchers from a number of institutions including The University of Manchester and the Max Planck Institute for Radio Astronomy in Germany found the object in orbit around a millisecond pulsar 40,000 light years away in a dense group of stars known as a globular cluster.
Millisecond pulsars are a type of pulsar (neutron star with pulses of radiation) that spin very rapidly – hundreds of times per second.
According to experts, it could be the first discovery of a radio pulsar – black hole binary – a pairing that could allow new tests of Einstein’s general relativity and open doors to the study of black holes.
UK project lead Ben Stappers, Professor of Astrophysics at The University of Manchester, said: “Either possibility for the nature of the companion is exciting.
“A pulsar–black hole system will be an important target for testing theories of gravity and a heavy neutron star will provide new insights in nuclear physics at very high densities.”
When a neutron stars – the ultra-dense remains of a dead star – acquire too much mass, they will collapse.
What they become after this, is the cause of much speculation, but it is believed that they could become black holes.
It is thought the total mass required for a neutron star to collapse is 2.2 times the mass of the Sun.
The lightest black holes created by these stars are much larger, at about five times more massive than the Sun, giving rise to what is known as the “black hole mass gap”.
The nature of objects in this mass gap is unknown and they are difficult to study.
Researchers say the latest discovery could help scientists finally understand these objects.
The discovery of the object was made while observing a large cluster of stars known as NGC 1851 located in the southern constellation of Columba, using the MeerKAT telescope.
Astronomers say it is so crowded that the stars can interact with each other, disrupting orbits and in the most extreme cases colliding.
They believe that a collision between two neutron stars may have created the massive object that now orbits the radio pulsar.
While the team cannot conclusively say whether they have discovered the most massive neutron star to date, the lightest black hole or even some new exotic star variant, they have uncovered something that will help to probe the properties of matter under the most extreme conditions in the universe.
The findings are published in the Science journal.