- 3583 - BLACKHOLE BINARIES - not many detected? Astronomers have not directly detected gamma or X-ray emissions from the pulsar in this binary star. The binary was discovered because we see a star with a day side that’s much hotter than the night side, orbiting around something every 62 minutes. This seems to point to it being a “black widow binary“.
--------------------- 3583 - BLACKHOLE BINARIES - not many detected?
- See Review 3582 about binary stars in general This review is about those special cases where one of the binaries is a blackhole.
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- A binary system 3,000 light years from Earth is a stellar oddity. It is called a “black widow binary” because a rapidly spinning neutron star, or pulsar, that is circling and slowly consuming a smaller companion star.
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- Astronomers know of about two dozen black widow binaries in the Milky Way. This newest candidate, “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.
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- This likely triple black widow is raising questions about how such a system could have formed. 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.
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- To detect the triple system astronomers used a new approach. 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.
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- Black widow binaries are powered by “pulsars” which are rapidly spinning neutron stars that are the collapsed cores of massive stars. Pulsars have a rotational period, spinning around every few milliseconds, and emitting flashes of high-energy gamma and X-rays in the process.
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- 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.
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- These systems are called “black widows” because of how the pulsar consumes the thing that recycled it.
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- 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.
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- Optical data was taken by the “Zwicky Transient Facility“, an observatory based in California that takes wide-field images of the night sky. The brightness of stars were changing dramatically by a factor of 10 or more, on a timescale of about an hour or less. These were signs that indicate the presence of a companion star orbiting tightly around a pulsar.
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- Astronomers then spotted this star whose brightness changed by a factor of 13, every 62 minutes, indicating that it was likely part of a new black widow binary.
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- 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. The one thing that was discovered is that we see a star with a day side that’s much hotter than the night side, orbiting around something every 62 minutes. This seems to point to it being a black widow binary.
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May 20, 2022 BLACKHOLE BINARIES - not many detected? 3583
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