Removing the hydrogen-rich layer from a main-sequence star exposes the helium-rich core. Such stripped helium stars are known at high and low masses, but not at intermediate masses, despite theoretical predictions that they should be common. In a new study, astronomers at the University of Toronto and elsewhere used ultraviolet photometry to identify candidates for stripped helium stars in two nearby dwarf galaxies, the Large and Small Magellanic Clouds. We observed 25 such candidate stars using optical spectroscopy. Most of these systems have been shown to be binary systems, with the companion star likely stripping the helium star of its outer hydrogen-rich layer.
An artist’s impression of a large-scale binary system. Image credit: ESO / M. Kornmesser / SE de Mink.
The hydrogen-rich outer layers of massive stars can be removed by interactions with binary companions.
Theoretical models predict that this separation would produce a population of hot helium stars with masses between two and eight times the mass of the Sun, but only one such system has been identified to date.
“This was a very large and noticeable hole. If these stars turn out to be rare, it could affect supernovae, gravitational waves, light from distant galaxies, and our theories for all these different phenomena. The whole framework is wrong,” said Dr Maria Draut, an astronomer at the university. of Toronto.
“This discovery shows that these stars actually exist.”
“In the future, we will be able to perform even more detailed physics on these stars.”
“For example, predictions of how many neutron star mergers we will see depend on the properties of these stars, such as how much material is ejected by stellar winds.”
“In the past, people have estimated it, but now for the first time they will be able to measure it.”
Dr. Drout and her colleagues designed a new study to look at the ultraviolet part of the spectrum, where very hot stars emit most of their light.
Astronomers used data from the Swift Ultraviolet/Optical Telescope to collect the brightness of millions of stars in the Large and Small Magellanic Clouds, the two closest galaxies to Earth.
They developed the first wide-field UV catalog of the Magellanic Clouds and used UV photometry to detect systems with unusual UV emissions indicating the possible presence of stripped stars.
They acquired optical spectroscopy with the Magellan Telescope at the Las Campanas Observatory from 2018 to 2022 and conducted pilot studies on 25 objects.
These stripped stars had high temperatures (60,000 to 100,000 K), high surface gravity, and hydrogen-depleted surfaces. Sixteen stars also showed binary motion.
Drout and his co-authors propose that these stars will eventually explode as hydrogen-depleted supernovae.
These objects, like the gravitational wave-emitting objects detected from Earth by the LIGO experiment, are also thought to be necessary for the formation of neutron star mergers.
In fact, researchers believe that some of the objects in the current sample are neutron stars or stripped stars with black hole companions.
These objects are on the verge of becoming double neutron stars or neutron star and black hole systems that may eventually merge.
“Many stars are part of a cosmic dance with partners, orbiting each other in binary star systems,” says Dr. Bethany Ludwig. He is a student at the University of Toronto.
“They are not solitary giants, but part of a dynamic duo, interacting and influencing each other throughout their lives.”
“Our research sheds light on these fascinating relationships, revealing a universe far more interconnected and active than previously imagined.”
“Just as humans are social beings, stars, especially massive stars, are rarely lonely.”
of result appear in the diary science.
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MR Drought other. 2023. Observed population of intermediate-mass helium stars separated by binaries. Science 382 (6676): 1287-1291; doi: 10.1126/science.ade4970
Source: www.sci.news
