50 million light-years away, a lighthouse in the distant spiral galaxy of NGC 5907 shines bright. It's so bright, in fact, that it might just be the brightest such light in the entire universe.
That lighthouse is NGC 5907 X-1, the spinning remains of a once-enormous star; a bizarre pulsar that is a thousand times brighter than previously thought possible for such an object, reports Phys.org.
Pulsars are highly magnetized, rotating neutron stars that emit a beam of electromagnetic radiation that appears to blink on and off as the object spins. They're extreme objects in many regards: their rapid spin rates, their powerfully luminous beams, their high density. But NGC 5907 X-1 is in a league of its own. Not only is it brighter than any pulsar ever discovered, but its rate of spin is increasing at an unprecedented rate.
"The discovery of this very unusual object, by far the most extreme ever discovered in terms of distance, luminosity and rate of increase of its rotation frequency, sets a new record ... and is changing our ideas of how such objects really 'work'," said Norbert Schartel, project science at ESA's XMM-Newton, an X-ray observatory.
How fast and bright is this pulsar?
Archival observations of the pulsar indicate that its spin rate has changed from 1.43 s per rotation in 2003, to 1.13 s in 2014. To put that in perspective, it would be like an Earth day shortening by five hours during a similar span of time. Meanwhile, the X-ray beam emanating from the collapsed star is so bright that it takes just one second to release the same amount of energy our sun releases every 3.5 years.
The pulsar is so unusual that scientists have had to double check to make sure it's not some other type of extreme object, like a black hole.
"Before, it was believed that only black holes at least 10 times more massive than our sun feeding off their stellar companions could achieve such extraordinary luminosities, but the rapid and regular pulsations of this source are the fingerprints of neutron stars and clearly distinguish them from black holes," said Gian Luca Israel, from INAF-Osservatorio Astronomica di Roma, Italy, lead author of the paper.
He added: "Only a neutron star is compact enough to keep itself together while rotating so fast."
The scientists suspect that the star might be getting its extreme brightness due to a strong, complex magnetic field close to its surface. In this scenario, accretion onto the neutron star surface could still be possible while generating such high luminosity. Even so, the fact that this object is up to 1,000 times brighter than previously believed possible for an accreting neutron star, it means our current understanding for how these intense objects work is insufficient.
More observation will be necessary to truly reveal NGC 5907 X-1's secrets. Until then, we're simply left to marvel at this dazzling beacon.
The study was published in the journal Science.