Astronomers discover a rare 'black widow' binary, with the shortest
orbit yet
The system is orbited by third stellar companion and may have originated
near the center of the Milky Way.

Date:
May 4, 2022
Source:
Massachusetts Institute of Technology
Summary:
Astronomers discovered a 'black widow binary' -- a rapidly spinning
neutron star circling and slowly consuming a smaller companion star.

Named ZTF J1406+1222, the pair has the shortest orbital period yet
identified, and is unique in that it appears to host a third star
that orbits around the two inner stars every 10,000 years.



FULL STORY ==========================================================================
The flashing of a nearby star has drawn MIT astronomers to a new and
mysterious system 3,000 light years from Earth. The stellar oddity appears
to be a new "black widow binary" -- a rapidly spinning neutron star, or
pulsar, that is circling and slowly consuming a smaller companion star,
as its arachnid namesake does to its mate.


========================================================================== Astronomers know of about two dozen black widow binaries in the Milky
Way. This newest candidate, named ZTF J1406+1222, has the shortest orbital period yet identified, with the pulsar and companion star circling each
other every 62 minutes. The system is unique in that it appears to host
a third, far-flung star that orbits around the two inner stars every
10,000 years.

This likely triple black widow is raising questions about how such
a system could have formed. Based on its observations, the MIT team
proposes an origin story: As with most black widow binaries, the triple
system likely arose from a dense constellation of old stars known as a
globular cluster. This particular cluster may have drifted into the Milky
Way's center, where the gravity of the central black hole was enough to
pull the cluster apart while leaving the triple black widow intact.

"It's a complicated birth scenario," says Kevin Burdge, a Pappalardo Postdoctoral Fellow in MIT's Department of Physics. "This system has
probably been floating around in the Milky Way for longer than the sun
has been around." Burdge is the author of a study appearing in Nature
that details the team's discovery. The researchers used a new approach
to detect the triple system.

While most black widow binaries are found through the gamma and X-ray
radiation emitted by the central pulsar, the team used visible light,
and specifically the flashing from the binary's companion star, to detect
ZTF J1406+1222.

"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
it came from the galactic center," Burdge says. "There's still a lot we
don't understand about it. But we have a new way of looking for these
systems in the sky." The study's co-authors are collaborators from
multiple institutions, including the University of Warwick, Caltech,
the University of Washington, McGill University, and the University
of Maryland.



==========================================================================
Day and night Black widow binaries are powered by pulsars -- rapidly
spinning neutron stars that are the collapsed cores of massive
stars. Pulsars have a dizzying rotational period, spinning around every
few milliseconds, and emitting flashes of high-energy gamma and X-rays
in the process.

Normally, pulsars spin down and die quickly as they burn off a huge
amount of energy. But every so often, a passing star can give a pulsar new life. As a star nears, the pulsar's gravity pulls material off the star,
which provides new energy to spin the pulsar back up. The "recycled"
pulsar then starts reradiating energy that further strips the star,
and eventually destroys it.

"These systems are called black widows because of how the pulsar sort of consumes the thing that recycled it, just as the spider eats its mate,"
Burdge says.

Every black widow binary to date has been detected through gamma and
X-ray flashes from the pulsar. In a first, Burdge came upon ZTF J1406+1222 through the optical flashing of the companion star.



==========================================================================
It turns out that the companion star's day side -- the side perpetually
facing the pulsar -- can be many times hotter than its night side,
due to the constant high-energy radiation it receives from the pulsar.

"I thought, instead of looking directly for the pulsar, try looking for
the star that it's cooking," Burdge explains.

He reasoned that if astronomers observed a star whose brightness was
changing periodically by a huge amount, it would be a strong signal that
it was in a binary with a pulsar.

Star motion To test this theory, Burdge and his colleagues looked through optical data taken by the Zwicky Transient Facility, an observatory
based in California that takes wide-field images of the night sky. The
team studied the brightness of stars to see whether any were changing dramatically by a factor of 10 or more, on a timescale of about an hour
or less -- signs that indicate the presence of a companion star orbiting tightly around a pulsar.

The team was able to pick out the dozen known black widow binaries,
validating the new method's accuracy. They then spotted 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.

They looked up the star in observations taken by Gaia, a space telescope operated by the European Space Agency that keeps precise measurements
of the position and motion of stars in the sky. Looking back through
decades old measurements of the star? from the Sloan Digital Sky Survey,
the team found that the binary was being trailed by another distant
star. Judging from their calculations, this third star appeared to be
orbiting the inner binary every 10,000 years.

Curiously, the astronomers have not directly detected gamma or X-ray
emissions from the pulsar in the binary, which is the typical way in which black widows are confirmed. ZTF J1406+1222, therefore, is considered
a candidate black widow binary, which the team hopes to confirm with
future observations.

"The one thing we know for sure is that we see a star with a day side
that's much hotter than the night side, orbiting around something every
62 minutes," Burdge says. "Everything seems to point to it being a black
widow binary. But there are a few weird things about it, so it's possible
it's something entirely new." The team plans to continue observing the
new system, as well as apply the optical technique to illuminate more
neutron stars and black widows in the sky.

This research was supported, in part, by the National Science Foundation.


========================================================================== Story Source: Materials provided by
Massachusetts_Institute_of_Technology. Original written by Jennifer
Chu. Note: Content may be edited for style and length.


========================================================================== Related Multimedia:
* Black_widow_pulsar_and_its_stellar_companion ========================================================================== Journal Reference:
1. Kevin B. Burdge, Thomas R. Marsh, Jim Fuller, Eric C. Bellm, Ilaria
Caiazzo, Deepto Chakrabarty, Michael W. Coughlin, Kishalay De, V. S.

Dhillon, Matthew J. Graham, Pablo Rodri'guez-Gil, Amruta D. Jaodand,
David L. Kaplan, Erin Kara, Albert K. H. Kong, S. R. Kulkarni,
Kwan-Lok Li, S. P. Littlefair, Walid A. Majid, Przemek Mro'z, Aaron
B. Pearlman, E. S. Phinney, Jan van Roestel, Robert A. Simcoe,
Igor Andreoni, Andrew J. Drake, Richard G. Dekany, Dmitry A. Duev,
Erik C. Kool, Ashish A.

Mahabal, Michael S. Medford, Reed Riddle, Thomas A. Prince. A
62-minute orbital period black widow binary in a wide hierarchical
triple. Nature, 2022; 605 (7908): 41 DOI: 10.1038/s41586-022-04551-1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/05/220504110446.htm

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