At an estimated distance of 140 parsecs (457 light years), the L-type subdwarf star CWISE J124909+362116.0 (J1249+36 for short) has a total velocity of at least 600 km/s, exceeding the local galactic escape velocity. Remarkably, the star may have been ejected from a globular cluster in the outer reaches of the Milky Way sometime in the past 10 to 30 million years.
A simulation of the hypothetical J1249+36 white dwarf binary ends with the white dwarf star exploding in a supernova. Image courtesy of Adam Makarenko / WM Keck Observatory.
J1249+36 was first discovered by a citizen scientist. Backyard Worlds: Planet 9 Program.
The star immediately stood out as its speed across the sky was initially estimated to be around 600 km/s.
This speed is fast enough for the star to escape the gravity of the Milky Way, making it a potential hypervelocity star.
To better understand the properties of J1249+36, Professor Adam Burgasser of the University of California, San Diego, and his colleagues used the W. M. Keck Observatory to measure its infrared spectrum.
These data revealed that the object is a rare L-type subdwarf star, a class of stars with an extremely low mass and temperature.
Spectral data and imaging data from multiple ground-based telescopes allowed the team to precisely measure J1249+36's position and velocity in space, and predict its orbit within the Milky Way galaxy.
“What makes this source so interesting is that its speed and orbit suggest it is moving fast enough to escape the Milky Way,” Professor Burgasser said.
The researchers focused on two scenarios to explain J1249+36's unusual orbit.
In the first scenario, J1249+36 was originally a low-mass companion to a white dwarf.
If a companion star is in a very close orbit with a white dwarf, it can transfer mass, causing periodic explosions called novae. If the white dwarf gathers too much mass, it can collapse and explode as a supernova.
“In this type of supernova, the white dwarf is completely destroyed, so the companion star is freed to fly away at the orbital velocity it was originally moving at, plus a bit of a supernova blast,” Prof Burgasser said.
“Our calculations show that this scenario holds true. However, because the white dwarf no longer exists and the remnants of the explosion that probably occurred millions of years ago have already dissipated, we have no conclusive evidence that this is its origin.”
In the second scenario, J1249+36 was originally a member of a globular cluster, a tightly bound group of stars that is immediately recognizable by its distinctive spherical shape.
The centers of these clusters are predicted to contain black holes with a wide range of masses.
These black holes can also form binary systems, and such systems prove to be great catapults for any star that happens to get too close to them.
“When a star encounters a black hole binary, the complex dynamics of this three-body interaction can cause the star to be thrown out of the globular cluster,” said Dr Kyle Kremer, an astronomer at the University of California, San Diego.
The scientists ran a series of simulations and found that, on rare occasions, these types of interactions can cause low-mass subdwarf stars to be ejected from globular clusters and follow orbits similar to the one observed in J1249+36.
“This is a proof of concept, but we don't actually know which globular cluster this star is from,” Dr Kremer said.
“By tracking J1249+36 back in time, we find that it lies in a very crowded part of the sky that may be hiding undiscovered star clusters.”
To determine whether one of these scenarios, or some other mechanism, can explain J1249+36's orbit, the team wants to take a closer look at its elemental composition.
For example, the explosion of a white dwarf star could produce heavy elements that could pollute J1249+36's atmosphere as they escape.
Stars in the Milky Way's globular clusters and satellite galaxies also have unique presence patterns that could shed light on the origins of J1249+36.
“We're basically looking for a chemical fingerprint that will pinpoint exactly what system this star came from,” says Roman Gerasimov, also of the University of California, San Diego.
“Whether J1249+36's high-speed movement is the result of a supernova, a chance encounter with a black hole binary, or some other scenario, its discovery offers astronomers a new opportunity to learn more about the history and dynamics of the Milky Way.”
The astronomers discovery this week's 244th Meeting of the American Astronomical Society In Madison, Wisconsin.
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Adam Burgasser others2024. A superfast L-type subdwarf star passes near the solar system. 224 AustraliaAbstract #3
Source: www.sci.news
