There are some strange objects lurking in our galaxy, and astronomers have spied an extreme new candidate, some 3,000 to 4,000 light-years away.
After probing the mysterious glow of light coming from the system, researchers have discovered they have an elusive ‘Black Widow’ star – a rapidly spinning pulsar that is kept alive by slowly eating away at its smaller companion star. .
Black Widow pulsars are the rarest – we know of only a dozen or more of them in the Milky Way. But it appears to be the most extreme, and arguably the most bizarre, example of that phenomenon we have ever found.
Designated ZTF J1406+1222, the binary system has the shortest orbital period ever observed, in which the ‘black widow’ and its prey orbit each other every 62 minutes.
Even more peculiar, the system appears to host a third, more distant star, which takes about 12,000 years to orbit the other two.
“This system is really unique as far as black widows go, because we found it with visible light, and because of its wide companion, and the fact that it came from the galactic center,” said MIT’s Department of Defense Kevin Burge, lead researcher and physicist at Physics.
Pulsars are produced when the cores of giant supergiant stars collapse into neutron stars. When these neutron stars become highly magnetized and spin rapidly, they become what we call pulsars.
Like ultra-bright lighthouses in the universe, pulsars spin very rapidly and emit X-rays and gamma rays shining toward us at intervals of more than a second, which can be counted in milliseconds. Usually pulsars spin faster and die young, because of how much energy they are dissipating.
But if a passing star gets close enough, the pulsar can slowly suck material out of it like a giant parasite, releasing enough energy to continue spinning and feeding the other star until until he eats it.
“These systems are called black widows because of how the pulsar consumes what it recycled, like a spider eating its mate,” says Burge.
In the past, astronomers have been alerted to these black widow systems via gamma rays or X-rays – bursts of high-frequency radiation carried by the pulsar itself.
But the team used a new technique to find ZTF J1406+1222: they looked for visible light coming from the eating star.
It turns out that the ‘day’ side of the companion star, which is locked with the black widow, may be several times hotter than the ‘night’ side, and this extreme variation in brightness is something that can be detected. Is.
To test this idea, the researchers used data from the Zwicky Transient Facility, an observatory in California, and were able to spot black widow systems we already know about, confirming that the technology works.
He then began looking for new black widows, and came across ZTF J1406+1222, where the companion star changes in brightness by a factor of 13 every 62 minutes.
This is the first time a black widow pulsar has been found like this, and it is part of what makes the discovery so exciting.
Above: Black Widow’s gamma-rays (magenta) heat up the fiery ‘day’ side of the star.
The other part, of course, is the mysterious system they stumbled upon.
Not only are the black widow pulsar and its prey locked in the tightest cannibalistic spiral observed to date, but when the team looked back through measurements of the star using the Sloan Digital Sky Survey, they saw that the system A rare low-metallicity cool subdwarf star, visible only once every 12,000 years in the orbit of the binary.
The presence of this distant third star could make the system a ‘triple’ black widow unheard of, and astronomers are scratching their heads about how the set-up might have formed in the first place.
Based on current observations, Burge and his colleagues have some ideas. Black Widow binaries arise from a dense constellation of older stars called globular clusters.
One of the leading hypotheses is that, if this particular cluster moved to the center of the galaxy, the gravity of our central black hole would have torn apart the cluster, leaving only the triple black widow.
“It’s a complicated birth scenario,” Burge says. “This system has probably been floating around in the Milky Way longer than the Sun.”
Weird even, while the team could detect ZTF J1406+1222 using visible light, when they looked back for gamma and X-rays, they couldn’t actually see it—which suggests that it may not actually be a black widow.
“One thing we know for sure is that we see a star with a day that is much hotter than at night, orbiting something every 62 minutes,” says Burge. “
“Everything points to it being a Black Widow binary. But there are some strange things about it, so it’s possible it’s something entirely new.”
The team plans to continue observing the system to get a better idea of what’s going on.
Interestingly, this neutron star ‘kick’ could be a prime candidate for learning more about physics. Astronomers know that when neutron stars form they get a ‘kick’ that accelerates them to high velocities.
But where this kick came from is not fully understood. The peculiar birth story of this mysterious system may shed light on this question.
“There’s still a lot we don’t understand about this. But we have a new way of looking for these systems in the sky.”
research has been published inNature.