A newly detected neutron star is the biggest ever discovered, and astronomers say it is right at the limit of collapsing itself into a black hole.
Neutron stars are relatively small, usually measuring about 15 miles across, but they can be incredibly dense.
They are created when giant stars die in supernovas and their cores collapse, leaving the remaining protons and electrons to melt into each other and form neutrons.
WVU physics professors Duncan Lorimer and Maura McLaughlin at the Green Bank Telescope. Pic: Scott Lituchy/West Virginia University
The snappily named J0740+6620 was detected some 4,600 light years from Earth (one light year is six trillion miles) and has been measured at more than twice the mass of the sun.
The sun is already a whopping 333,000 times the mass of the Earth, and scientists who discovered J0740+6620 have said that if it was any denser it would crush itself down into a black hole.
Professor Maura McLaughlin, who co-authored a paper published in the Nature Astronomy journal, explained that the neutron star was uncovered via the Green Bank Telescope in West Virginia in the US.
She said: “At Green Bank, we’re trying to detect gravitational waves from pulsars.
“In order to do that, we need to observe lots of millisecond pulsars, which are rapidly rotating neutron stars.”
The mass of J0740+6620 was measured through a phenomenon known as Shapiro Delay, when gravity from a nearby white dwarf warps the surrounding space and makes its pulses travel a bit further.
As the pulses made their way through the distorted space, the researchers were able to measure the mass of both the white dwarf and the neutron star.
Its enormous size left the team stunned and raised further questions about just how massive they can be.
Professor McLaughlin said: “These stars are very exotic. We don’t know what they’re made of and one really important question is: ‘How massive can you make one of these stars?’
“It has implications for very exotic material that we simply can’t create in a laboratory on Earth.”