The W.M. Keck Observatory on Maunakea announced a pair of celestial discoveries Tuesday, including the heaviest neutron star ever seen.
According to a Keck news release, a neutron star about 3,000 light years from Earth first discovered in 2017 has been determined to have the mass of 2.35 suns, condensed inside a body only 15-20 kilometers (about 10-12 miles) in diameter. The star is therefore the densest known object observable from Earth.
Neutron stars — the collapsed cores of super-giant stars that die in supernovas — are some of the densest matter in the universe, composed of material that weighs 10 billion tons per cubic inch. The star in question, designated PSR J0952-0607, is believed to have become so massive by absorbing the mass of a companion star.
Absorbing its companion has also conferred vast amounts of energy to the neutron star and set it spinning 707 times per second, one of the fastest-rotating neutron stars yet observed.
Astronomers Alex Filippenko and Roger Romani, respectively professors at the University of California, Berkeley, and Stanford University, have studied “black widow stars” — named after the black widow spider that devours its mate — to determine the upper limit on how large neutron stars can grow. With this discovery, they said, that upper limit has been proven to be at least 2.35 solar masses.
Neutron stars collapse into black holes when they reach a certain mass threshold. Filippenko said in a statement that unless they can find other black widow stars with even greater mass, then “it tightens the argument that 2.3 solar masses is the true limit, beyond which they become black holes.”
The discovery also helps astronomers understand the inner workings of neutron stars, as a higher upper mass limit would preclude theories that the stars’ interiors are composed of exotic quantum states of matter, Romani said.
Meanwhile, Keck also announced Tuesday that a team of astronomers using several telescopes around the world, including Keck Observatory and Gemini North on Maunakea, discovered the source of a series of deep-space energy bursts: several distant galaxies up to 10 billion light-years away.
Such energy bursts — called gamma-ray bursts, formed during the collisions of neutron stars — typically originate from galaxies dense with stars, but some bursts have appeared to originate from the nothingness of space. However, using seven powerful telescopes around the world, astronomers were able to discover galaxies that were previously undetectable as the source of the bursts.
The discovery sheds light on the chemical evolution of the universe. If Earth detected a gamma-ray burst from 10 billion light-years away, then that means neutron star collisions happened at least 10 billion years ago, and because those collisions are necessary to produce heavy metals such as gold, the discovery means that the young universe was richer in those metals than previously thought.
Email Michael Brestovansky at mbrestovansky@hawaiitribune-herald.com.
