Superheavy neutron star that was only present for a brief period of time is discovered by scientists

 Gamma-ray burst observations and computer simulations together give fresh light on merging neutron stars.

By Chris Young

January 11, 2023 60:41 AM EST

The fast growth of two merging neutron stars into a superheavy neutron star, which subsequently collapsed into a black hole, was discovered by astronomers after they combed through historical data of brief gamma-ray bursts (GRBs).

According to a blog post from NASA, this entire event took place in a fraction of a second and has a lot to teach us about the fleeting nature of neutron stars and the development of massive black holes.

A black hole is produced when two neutron stars combine.

Since the Big Bang itself, gamma-ray bursts have been regarded to be the most potent and intense explosions ever seen by mankind. A large star that has run out of fuel collapses in on itself to produce an exceedingly dense, compact star, which is how a neutron star develops. Above a certain mass, neutron stars that are generally the size of Manhattan and have a mass bigger than our sun collapse into black holes.

The 700 brief GRBs discovered by NASA's Neil Gehrels Swift Observatory, the Fermi Gamma-ray Space Telescope, and the Compton Gamma-Ray Observatory were examined by the researchers for GRB signals. Compton was deorbited and destroyed in the Earth's atmosphere in the year 2000, hence it is no longer in existence.

In two bursts seen by Compton in the early 1990s, the researchers discovered gamma-ray patterns suggestive of two neutron stars merging and ultimately generating a black hole.

Cole Miller, an astronomy professor at UMCP and a co-author of the article, stated, "We know that brief GRBs arise when orbiting neutron stars smash together, and we know that they eventually collapse into a black hole, but the specific sequence of events is not well known. We are interested in finding out more about the evolution of the young black hole's jet of rapidly moving particles that releases a strong flash of gamma rays, the most energetic kind of light, at some time.

Mega neutron stars spin over 78,000 times per minute, or nearly twice as rapidly as J1748-2446ad, the fastest pulsar yet seen, according to NASA. They can very briefly support themselves against further collapse thanks to this quick rotation. They barely last a few tenths of a second before disappearing into a black hole, though.

Neutron stars will be better understood thanks to future gravitational wave detectors.

Even though they frequently last only two seconds, short GRBs are so strong that they may be seen from more than a billion light-years distant. Meanwhile, gravitational waves from merging neutron stars may be seen by Earth-based ground-based observatories.

The researchers discovered they could adapt their GRB observations to an anticipated shift in gravitational wave frequency when the neutron star fused using computer models. Because of this, they were able to see the merging stars, which were too weak to be seen by most gravitational wave observatories. These enormous merging stars were discovered thanks to two brief GRBs that happened on July 11th, 1991 and November 1st, 1993.

Gravitational wave observatories are anticipated to become significantly more sensitive by the 2030s, enabling them to provide fresh light on the transitory nature of neutron stars. Up until then, the most comprehensive understanding of cosmic objects comes from gamma-ray observations combined with computer modelling.

A study published in the journal Nature describes the results in full.

Study adstract:

Binary neutron star mergers, which are multimessenger astronomical occurrences that have been recorded in both gravitational waves and the multiband electromagnetic spectrum1, are connected to short gamma-ray bursts (GRBs). A dynamically evolving and short-lived neutron star may be created after the merger, existing for roughly 10-300 ms before collapsing to a black hole2,3. This depends on the masses of the stars in the binary and the specifics of their largely unknown equation of state. Different groups' numerical relativity simulations consistently show broad power spectral features in the 1–5 kHz range in the post–merger gravitational wave signal4,5,6,7,8,9,10,11,12,13,14, which is inaccessible to third-generation ground-based detectors now but might be visible in the coming decade15,16,17. This suggests that in a subset of occurrences in which a neutron star is produced just before the ultimate collapse to a black hole,18,19,20,21 there may be a potential of quasiperiodic modulation of the radiated gamma rays. Here, we show two such signals that were discovered in the historical Burst and Transient Source Experiment (BATSE) data and were found in the brief bursts GRB 910711 and GRB 931101B. These signals are consistent with the expectations of numerical relativity.