Scientists have found a strange "pulsar" deep in space that could solve some of the universe's most fundamental mysteries.
The discovery could help us understand how dead stars collide and the universe's expansion, according to the researchers who found it.
The pulsar – a neutron star "lighthouse" deep in space that sends out blasts of radio energy as it spins around – is locked in a tight orbit with another star.
Eventually, the two stars will collide, sending out energy in gravitational waves that will disturb spacetime in ways that can be detected across the universe.
Scientists have found such pulsars, and dead neutron stars locked in binary systems, before. But the newly discovered object is the first time that a pulsar has been found in such a strange relationship, with one of the pair far larger than the other.
It's that unusual difference that scientists hope can be used to provide important clues about some of the deepest, unsolved mysteries of the universe. Those include a better estimate of the Hubble constant, or the rate of expansion of the universe, as well as what the objects are actually made of.
Astronomers hope that the powerful blast of "disruption" caused when the stars collide will allow them to see it from Earth, using both gravitational wave detectors and more traditional telescopes. Among other things, that will allow them to get a better measure of the Hubble constant – which is especially useful given that the two main ways of measuring that value are currently in contradiction.
"Such a disruption would allow astrophysicists to gain important new clues about the exotic matter that makes up the interiors of these extreme, dense objects," said Paulo Freire from the Max Planck Institute for Radio Astronomy.
"This matter is still a major mystery - it's so dense that scientists still don't know what it is actually made of. These densities are far beyond what we can reproduce in Earth-based laboratories."
The vast difference between the two neutron stars is not something that scientists had expected to find until now.
"Most theories about this event assumed that neutron stars locked in binary systems are very similar in mass," said lead researcher Dr Robert Ferdman, from UEA's School of Physics, in a statement.
"Our new discovery changes these assumptions. We have uncovered a binary system containing two neutron stars with very different masses.
"These stars will collide and merge in around 470 million years, which seems like a long time, but it is only a small fraction of the age of the Universe.
"Because one neutron star is significantly larger, its gravitational influence will distort the shape of its companion star - stripping away large amounts of matter just before they actually merge, and potentially disrupting it altogether.
"This 'tidal disruption' ejects a larger amount of hot material than expected for equal-mass binary systems, resulting in a more powerful emission.
"Although GW170817 can be explained by other theories, we can confirm that a parent system of neutron stars with significantly different masses, similar to the PSR J1913+1102 system, is a very plausible explanation.
"Perhaps more importantly, the discovery highlights that there are many more of these systems out there - making up more than one in 10 merging double neutron star binaries."
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