Astronomers Discover a Mysterious “Black Widow” Binary – With the Shortest Orbit Yet

The flashing of a nearby star drew the attention of a team of astronomers, who discovered that it is part of a rare and mysterious system. As they report in a paper published recently in the journal Nature, the stellar oddity appears to be a “black widow binary” — a type of system consisting of a rapidly spinning neutron star, or

Astronomers know of about two dozen black widow binaries in the

Normally, pulsars spin down and die quickly as they burn off a huge amount of energy. But occasionally, the pulsar’s gravity can pull material off of a passing wayward star, providing new energy to spin the pulsar back up. The “recycled” pulsar then starts reradiating energy that further strips the star and eventually destroys it.

While most black widow binaries are found through the gamma and X-ray radiation emitted by the central pulsar, the team used visible light from the flashing from the binary’s companion star to detect ZTF J1406+1222. Burdge recognized that the companion star’s so-called “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. He reasoned that if astronomers observed a star whose brightness was changing periodically by a large amount, it would be a strong sign that it was in a binary with a pulsar.

To test this theory, Burdge and his co-authors studied the brightness of stars from ZTF data to see whether any were changing dramatically by a factor of 10 or more, and on a time scale of about an hour or less. The team was able to pick out the dozen known black widow binaries, validating the new method’s

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

“Everything seems to point to it being a black widow binary,” Burdge said. “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.

“Identifying this black widow binary with ZTF alone suggests that we should be able to find even more such systems in a few years when the even more powerful Vera C. Rubin Observatory comes online,” said Bellm.

For more on this discovery, see Astronomers Discover Mysterious “Black Widow” Binary System.

Reference: “A 62-minute orbital period black widow binary in a wide hierarchical triple” by 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 Rodríguez-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 Mróz, 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 and Thomas A. Prince, 4 May 2022, Nature.
DOI: 10.1038/s41586-022-04551-1

Co-authors include scientists at the Astronomers Discover a Mysterious “Black Widow” Binary – With the Shortest Orbit Yet