Not much can be accomplished in a few hundredths of a second. However, neutron stars that have been seen in two gamma ray bursts have more than enough time to teach us a thing or two about life, death, and the birth of black holes.
Shaken by an archive of high-energy flashes in the night sky, astronomers have recently discovered patterns in the oscillations of light left by two stars in a different setting, marking a pause in the journey from a super-dense object to an infinite pit of darkness.
That delay — somewhere between 10 and 300 milliseconds — technically equates to two recently formed, mega-friendly neutron stars, which researchers suspect were each fast enough to briefly undergo an inevitable fate as black holes.
“We know that short GRBs form when orbiting neutron stars collide together and we know that they eventually fall into a black hole, but the precision of the events is not well understood,” says Cole Miller, an astronomer at the University of Maryland College. Park (UMCP) in the US.
“We found these gamma-ray patterns in two eruptions observed by Compton in the early 1990s.”
For nearly 30 years, the Compton Gamma Ray Observatory has circled the Earth and collected the glow of X-rays and gamma rays that spilled from distant cataclysmic events. That archive of high-energy photons contains a record of information about things like colliding neutron stars, which emit powerful pulses of radiation known as gamma-ray bursts.
Neutron stars are the real beasts of the universe. They double the mass of our Sun within a mass of space roughly the size of a small city. This not only makes the material strange, so that by forcing electrons into protons it turns into a heavy impulse of neutrons, it can generate magnetic fields in no other way than in the universe.
When spun into high rotation, these fields can accelerate particles to ridiculously high speeds, forming polar bursts that appear as “pulses” like superimposed lighthouses.
Neutron stars form when more ordinary stars (about 8 to 30 times the mass of our Sun) burn up the last of their fuel, leaving a core of about 1.1 to 2.3 solar masses, too cool to withstand the pressure of their gravity.
Add a bit of mass – like cramming two neutral stars together – and even the ones that don’t have enough of them can’t resist the hum of gravity fields urging it to crush the living physics out of the dead star. From the dense mass of particles, whatever strange horror is gathered, which becomes the heart of the black hole.
The basic theory of the process is pretty straightforward, just putting general limits on how heavy a neutron star can be before it collapses. For cold, non-circulating balls of matter, this upper limit is just under three solar masses, but it also involves implications that the path from the neutron star to the black hole would be a less than direct path.
For example, last year physicists announced the observation of a gamma-ray burst GRB 180618A, detected again in 2018. The burst’s afterglow marks a magnetically-charged neutron star called a magnet, along with its signature. mass closer than that of two stars converging.
A day later this heavy weight of neutrons was no longer there, no doubt succumbing to its extraordinary mass and transforming into something not even light can escape.
How it could resist gravity for so long is a mystery, although its magnetic fields may have fulfilled its role.
These two could also be found in a few new discoveries.
A more accurate term for the pattern observed in gamma-ray bursts given by Compton in the early 1990s is quasiperiodic oscillation. The mixture of frequencies that rise and fall in the signal can be explained to describe the final moments of massive objects as they surround each other and then collide.
From what the researchers can tell, each collision with an object about 20 percent larger than the current record-holding massive neutron star — hitting 2.14 times the mass of our Sun — counted. They were also twice the diameter of a typical neutron star.
Interestingly, the extraordinary objects were rotating at a rate of nearly 78,000 times per minute, far faster than the record held by pulsar J1748-2446, which is a mere 707 revolutions per second.
A few rotations of each neutron star in its short half-second life could pull down enough angular momentum to fight the implosion of its gravity.
How this can apply to other neutron star mergers, further confusing the limits of stellar collapse and black hole generation, is a question for future research.
This research was published in nature.
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