Mysterious Object May Set New Records for Black Holes or Neutron Stars
Astronomers have discovered a cosmic object that could be a black hole or neutron star, or something new to science.
The pulsar, a rotating neutron star that emits a beam of light every 6 milliseconds, which orbits the unidentified object 40,000 light-years away inside a dense globule of stars called NGC 1851, helped astronomers find it.
According to the researchers, the new entity is in the historical “mass gap” between black holes and neutron stars, so it could be either. The researchers’ findings were published in the Science journal on January 18th.
“Either possibility for the nature of the companion is exciting,” lead author Ben Stappers, an astrophysics professor at the University of Manchester in the United Kingdom, 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 in nuclear physics at very high densities.”
Both black holes and neutron stars are stellar corpses left behind when massive stars explode violently, known as supernovae. Despite being born in the same way, the two types of objects may have vastly different masses: Supermassive black holes can weigh billions of suns, whereas neutron stars rarely exceed three solar masses.
However, the lightest black holes and the heaviest neutron stars can appear very similar from a distance. For most of astronomy’s history, scientists could only see neutron stars twice the mass of the sun and black holes as light as five solar masses, leaving everything in between a mystery.
The Laser Interferometer Gravitational-Wave Observatory (LIGO) finally bridged the mass gap in 2019 by detecting ripples in space-time caused by the falling of a light black hole or a heavy neutron star.Nonetheless, detections of mass-gap-filling objects using traditional light-based telescopes have remained difficult.
Unlocking Celestial Mysteries
Astronomers used the MeerKAT radio telescope in South Africa to scan the NGC 1851 globular cluster, a crowded blob of stars so densely packed that cosmic furnaces can occasionally knock each other out of their orbits and even collide.
Faint radio pulses repeating 170 times per second drew astronomers’ attention to a pulsar, and by observing the subtle changes in its highly regular “ticks,” the scientists mapped its orbital motion. This discovery showed that the pulsar was in a binary system and was orbiting an object with a mass of approximately 3.9 times that of the Sun, which is located in the middle of the mass gap.
It is unclear whether the object is the most massive neutron star known, the lightest black hole, or an exotic star husk that has yet to be characterized. However, the researchers stated that further investigation could help them test our current theories of matter.
“We’re not done with this system yet,” co-author Arunima Dutta, a doctoral student at the Max Planck Institute for Radio Astronomy in Bonn, Germany, said in the statement. “Uncovering the true nature of the companion will be a turning point in our understanding of neutron stars, black holes, and whatever else might be lurking in the black hole mass gap.”
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