Astronomers have discovered 21 “one-in-a-million” binary star systems in which a sun-like star orbits an extremely dense, compact, hidden “dead star” called a neutron star.
One of Neutron Star Discovered within this binary group is one of the most massive dead stars of its type ever observed.
We are used to single stars like us, SunAt least half of the stars with the mass of the Sun Binary SystemThis percentage increases to 75% in more massive stars, resulting in neutron stars and Black Hole Binary star systems (born from the death of a massive star) also exist, in binary relationships with other dead or massive stars.
However, one binary configuration that has proven to be extremely rare is one in which a sun-like star orbits a neutron star. European Space Agency(ESA) Gaia The spacecraft has allowed astronomers to discover a new population of these elusive binary star systems.
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Neutron stars often orbit normal stars like the Sun, but they are so close that the dead star feeds on its Sun-like companion. Space vampire. What makes this binary system of neutron stars and normal stars so special is that they are so widely separated, which could call into question our understanding of how such systems come into being.
“According to the binary evolution model, neutron stars and normal binaries are primarily born in tight orbits, Neutron Star and Companion “It looks like they’re nearly in contact,” Kareem El Badry, a research scientist at the Harvard-Smithsonian Center for Astrophysics (CfA) and leader of the discovery team, told Space.com. “These binaries are much wider than this, at distances of about 300 to 1,000 times the size of the star.”
“This means that an alternative neutron star-normal star formation model may be needed.”
These neutron stars resist cannibalization by their companions.
A neutron star is born When a star eight times more massive than the Sun runs out of fuel for nuclear fusion and the outward pressure that supported the star against the inward pressure of its own gravity is no longer present.
When the core of such a star collapses, its outer layers become a mass of Supernova explosion. This leaves behind a stellar core that is one to two times the mass of the Sun and about 12 miles (20 kilometers) wide.
One of the newly discovered neutron stars lies right on the edge of the theoretical mass range, with a mass 1.9 times that of the Sun, making it one of the most massive neutron stars ever observed.
The really important thing about these binaries is that they raise the question of how they managed to survive after one star turned into a neutron star.
During this process, the massive star may have violently attacked its smaller companion, possibly even engulfing it temporarily. A neutron star explodes into a supernovaCurrent models suggest that the smaller star would have been “kicked away,” ending the binary’s existence.
“The discovery of these new systems indicates that at least some binary star systems survive these cataclysmic processes, even though models cannot yet fully explain how they work,” El Badry said.
When neutron stars are found orbiting “living” main sequence stars, the neutron stars tend to strip material from the main sequence star. Space vampire. Such binary systems are remarkable because the neutron star and main sequence star are close enough to each other to facilitate the transfer of matter.
Because this material has angular momentum, it cannot fall straight into the neutron star, but insteadAccretion diskMaterial is gradually fed to the neutron star from the accretion disk, but when it hits the surface the results are far from gentle. Cannibal Prey This process can release as much energy in one second as it takes the sun a million years to radiate.
Much of this energy release is powerful Fast jet planes, These neutron star-feeder binaries are extremely conspicuous to astronomers, especially at x-ray and radio wavelengths. Electromagnetic spectrumBut more distant binaries with quiet, faint neutron stars are harder to find.
“Most neutron star binaries are discovered through x-ray or radio data resulting from current or past accretion,” El Badri said. “These neutron stars are harder to find because they’re not accreting anything and don’t emit detectable levels of x-ray or radio waves.”
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Gaia These discoveries are possible thanks to the ability to precisely measure the positions and motions of billions of stars against the background sky. Precise tracking of the stellar motions reveals the gravitational influence of the dark neutron star companion on these visible components of the binary system, even though the two objects are far apart.
This effect is detected as a slight wobble in the star’s motion caused by the gravitational pull of its companion star – the first time a neutron star has been detected due to its gravitational influence alone.
“Gaia can detect extremely small movements of Sun-like stars in the sky and measure their positions with an accuracy equivalent to the width of a human hair from 3,000 miles away. [5,000 kilometers] “This is the only astronomy facility left right now,” El Badry said.
Gaia is actually more sensitive to the wider orbits and longer orbital periods of these systems. El Badry explained that if these neutron stars were closer to their companions, the wobbles they caused would have been too small for ESA’s spacecraft to detect.
Gaia was also helped by the fact that these binary stars are only about 3,000 light years away from Earth. This may seem like a very long distance, but milky way, It is relatively small.
The detection of 21 such systems is a big deal, but it doesn’t change the idea that widespread binary systems between neutron stars and regular stars are rare in the universe, El Badry said.
“We estimate that about one in a million solar-type stars orbit neutron stars in wide orbits,” he explained, “but we weren’t really surprised by the discovery. We had hoped that such stars would be detectable with Gaia, and characterizing these objects has been one of the main projects of my research group for the past few years.”
El Badri explained that the next step in this research is for the team to create models to explore the formation and future evolution of binaries between neutron stars and regular stars.
CfA researchers also plan to use Gaia to search for widespread binaries with a normal star and a non-perturbative black hole.
“these Black hole binary “Our models of binary evolution are clearly flawed. Discovering more of these dark companions and comparing their population statistics with the predictions of different models will help us understand how binaries form,” El Badry concluded.
Gaia has already demonstrated its detection capabilities A quiet, dark black hole.
In April 2023, Gaia discovered two dark black holes. Gaia BH1 and Gaia BH2are 1,560 and 3,800 light years away from Earth, respectively. This year, the space telescope discovered Gaia BH3, just 2,000 light years away. These are the three closest black holes to Earth discovered so far.
The research team’s study was published on July 15th. Open Astrophysics Journal.
