- 3578 - - BLACKHOLE GALAXIES - and black widows? The flashing of a nearby star 3,000 light years from Earth is a stellar oddity that appears to be a new “black widow binary”. This is a rapidly spinning neutron star, or pulsar, that is circling and slowly consuming a smaller companion star.
---------------- 3578 - BLACKHOLE GALAXIES - and black widows?
- 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.
-
- 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.
-
- While most black widow binaries are found through the gamma and X-ray radiation emitted by the central pulsar, this team used visible light, and specifically the flashing from the binary’s companion star. This system is really unique as far as black widows go, because they found it with visible light, and because of its wide companion, and the fact it came from the galactic center.
-
- The black widow binaries are powered by pulsars, which are rapidly spinning neutron stars that are the collapsed cores of massive stars. Pulsars have a rapid 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 called “black widows” because of how the pulsar sort of consumes the thing that recycled it, just as the spider eats its mate. Every black widow binary to date has been detected through gamma and X-ray flashes from the pulsar.
-
- This pulsar was discovered through the optical flashing of the companion star. 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.
-
- They 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. These are the signs that indicate the presence of a companion star orbiting tightly around a pulsar.
-
- They were 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.
-
- 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 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.
-
- Astronomers detect the signature of various elements in supernova explosions. These elements are layered like an onion pre-supernova. Hydrogen is found in the outermost layer of a star, and if no hydrogen is detected in the aftermath of the supernova, that means it was stripped away before the explosion occurred.
-
- These new Hubble observations provide the best evidence yet to support the theory that an unseen companion star siphons off the gas envelope from its partner star before it explodes.
-
- Hubble's Wide Field Camera 3 was used to study the region of supernova in ultraviolet light. Astronomers saw the light of the supernova fading over time from 2016 to 2020. Another nearby source of ultraviolet light at the same position maintained its brightness. This underlying source of ultraviolet emission is what the team proposes is the surviving binary companion.
-
- Hubble saw two peaks in the ultraviolet light, rather than just the one typically seen in most supernovae. One explanation for this double brightening was that the second peak shows when the supernova's shock wave hit a companion star.
-
- The evolution astronomers propose for supernova (SN) 2013ge:
-
-------------------------- 1) A binary pair of massive stars orbit one another.
-
-------------------------- 2) One star ages into its red giant stage, getting a puffy outer envelope of hydrogen that its companion star siphons off with gravity. This is why Hubble found no trace of hydrogen in the supernova debris.
-
-------------------------- 3) The stripped-envelope star goes supernova, jostling but not destroying its companion star. After the supernova, the dense core of the former massive star remains either as neutron star or black hole.
-
-------------------------- 4) Eventually the companion star also ages into a red giant, maintaining its outer envelope, some of which came from its companion.
-
-------------------------- 5) The companion star also undergoes a supernova.
-
-------------------------- 6) If the stars were close enough to each other not to be flung from their orbits by the supernova blast wave, the remnant cores will continue to orbit one another and eventually merge, creating gravitational waves in the process.
-
- Unlike supernovae that have a puffy shell of gas to light up, the progenitors of fully stripped-envelope supernovae have proven difficult to identify in pre-explosion images.
-
- As a massive star itself, “SN 2013ge's” companion is also destined to undergo a supernova. Its former partner is now likely a compact object, such as a neutron star or black hole, and the companion will likely go that route as well.
-
- The closeness of the original companion stars will determine if they stay together. If the distance is too great, the companion star will be flung out of the system to wander alone across our galaxy, a fate that could explain many solitary supernovae.
-
- However, if the stars were close enough to each other pre-supernova, they will continue orbiting each other as black holes or neutron stars. In that case, they would eventually spiral toward each other and merge, creating “gravitational waves” in the process.
-
- Gravitational waves are waves or ripples in the fabric of spacetime itself, predicted by Albert Einstein in the early 20th century. Gravitational waves were first directly observed by the “Laser Interferometer Gravitational-Wave Observatory“.
-
- There is great potential beyond just understanding the supernova itself. Since we now know most massive stars in the universe form in binary pairs, observations of surviving companion stars are necessary to help understand the details behind binary formation, material-swapping, and co-evolutionary development.
-
- Understanding the lifecycle of massive stars is particularly important to us because all heavy elements are forged in their cores and through their supernovae. Those elements make up much of the observable universe, including life as we know it.
-
May 14, 2022 - BLACKHOLE GALAXIES - and black widows? 3578
----------------------------------------------------------------------------------------
----- Comments appreciated and Pass it on to whomever is interested. ---
--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for copies or Index of all reviews
--- to: ------ jamesdetrick@comcast.net ------ “Jim Detrick” -----------
--------------------- --- Sunday, May 15, 2022 ---------------------------
No comments:
Post a Comment