Scientists discovers a Mysterious object 3,000 light years from Earth
An international team, in which the Institute of Astrophysics of the Canary Islands (IAC) and the University of La Laguna (ULL) participate, has discovered a new and mysterious object 3,000 light years from Earth. The oddity appears to be a stellar ‘black widow’, a pulsar – a rapidly spinning neutron star – that circles a smaller companion star while ruthlessly consuming it. It receives that name because its behavior is reminiscent of that of the large female spider that devours the smaller male after mating.
Astronomers know of about two dozen black widow binaries in the Milky Way. But this , called ZTF J1406+1222, has the shortest orbital period yet identified: the pulsar circles the companion every 62 minutes.
The object is also unique in that it appears to host a distant third star that orbits the two inner stars every 10,000 years.
The team, led by the Massachusetts Institute of Technology (MIT), believe the triple system likely arose from a dense constellation of old stars known as a globular cluster. This particular cluster may have drifted toward the center of the Milky Way, where the gravity of the central black hole was enough to pull the cluster apart and leave the triple black widow intact.
“It’s an easy calving scenario,” admits Kevin Burdge of the MIT Department of Physics and author of the discovery study, published in the journal Nature. “This system has probably been floating around in the Milky Way for longer than the Sun,” he adds.
The researchers used a new approach to detect the triple system. While most black widow binaries are found through gamma and X-ray radiation emitted by the central pulsar, the team used visible light, and specifically the flickering of the companion star, to detect a ZTF J1406+1222.
“This object is really unique when it comes to black widows, because we found it in visible light, and because of its broad companion, and the fact that it’s coming from the galactic center,” says Burdge. As he explains, “there’s still a lot we don’t understand about it. But we have a new way to look for these systems in the sky.”
Normally, pulsars quickly spin and die as they burn up a large amount of energy. But every once in a while, an unsuspecting star passing by can give it a new lease of life. As it approaches, the pulsar’s gravity pulls material from the star, giving it new energy to spin. The boosted pulsar then begins to re-radiate energy that further strips the little star and ultimately destroys it.
“These systems are called black widows because of the way the pulsar consumes the star, much like the spider comes to its mate,” explains Burdge.
To date, these systems have been detected through the pulsar’s X-ray and gamma-ray flares. But this time, for the first time, Burdge got another method: he looked at the optical flicker of the companion star.
It turns out that the companion’s day side, the side that perpetually faces the pulsar, can be many times hotter than the night side, due to the constant high-energy radiation it receives from the pulsar. Burdge reasoned that if astronomers observed a star whose brightness periodically changed by a large amount, it would be a strong signal that it was in a binary system with a pulsar.
To test this theory, the scientist and his colleagues analyzed optical data taken by the Zwicky Transient Facility, a California-based observatory that takes wide-field images of the night sky. The team mapped the brightness of stars to see if any were changing bright by a factor of 10 or more, on a time scale of about an hour or less, signs that indicate the presence of a companion star orbiting alongside a pulsar.
The team was able to select the dozen or so known black widow binaries, validating the accuracy of the new method. They then saw a star whose brightness changed by a factor of 13 every 62 minutes, indicating that it was likely part of a new black widow binary, which they labeled ZTF J1406+1222.
Interestingly, astronomers have not directly detected gamma or X-ray emissions from the pulsar in binary, which is the typical way black widows are confirmed. So ZTF J1406+1222 is therefore still considered a black widow binary candidate, which the team hopes to confirm with future observations.