HE 0437-5439 is a massive, unbound

hypervelocity star In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space. Stellar kinematics encompasses the measurement of stellar velocities in the Milky Way and its satellites as well as ...

(HVS), also called HVS3. It is a

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

B-type

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

located in the

Dorado constellation Dorado () is a constellation in the southern sky. It was named in the late 16th century and is now one of the 88 modern constellations. Its name refers to the dolphinfish (''Coryphaena hippurus''), which is known as ''dorado'' in Spanish, althou ...

. It was discovered in

2005 File:2005 Events Collage V2.png, From top left, clockwise: Hurricane Katrina in the Gulf of Mexico; the Funeral of Pope John Paul II is held in Vatican City; "Me at the zoo", the first video ever to be uploaded to YouTube; Eris was discovered in ...

with the Kueyen telescope, which is part of the European Southern Observatory's

Very Large Telescope The Very Large Telescope (VLT) is a telescope facility operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. It consists of four individual telescopes, each with a primary mirror 8.2 m across, ...

array. HE 0437-5439 is a young star, with an age of around 30 million years. The mass of the star is almost nine times greater than the mass of the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

and the star is located 200,000 light years away in the direction of the

Dorado Dorado () is a constellation in the southern sky. It was named in the late 16th century and is now one of the 88 modern constellations. Its name refers to the dolphinfish (''Coryphaena hippurus''), which is known as ''dorado'' in Spanish, altho ...

constellation, 16 degrees northwest of the

Large Magellanic Cloud The Large Magellanic Cloud (LMC), or Nubecula Major, is a satellite galaxy of the Milky Way. At a distance of around 50 kiloparsecs (≈160,000 light-years), the LMC is the second- or third-closest galaxy to the Milky Way, after the ...

(LMC) and farther away than the LMC. The star appears to be receding at an extremely high velocity of , or . At this speed, the star is no longer

gravitationally In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stron ...

bound and will leave the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

galaxy system and escape into

intergalactic space Outer space, commonly shortened to space, is the expanse that exists beyond Earth and its atmosphere and between celestial bodies. Outer space is not completely empty—it is a near-perfect vacuum containing a low density of particles, predo ...

. It was thought to have originated in the LMC and been ejected from it soon after birth. This could happen if it originally was one of a pair of stars and if there is a

supermassive black hole A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions of times the mass of the Sun (). Black holes are a class of astronomical obj ...

in the LMC. In 2010 a study was published in which its

proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...

was estimated using images from the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...

from 2006 and 2009. This ruled out the possibility that the star came from the Large Magellanic Cloud, but was consistent with the hypothesis that it was ejected from the center of the

. Given its velocity, this would have occurred 100 million years ago. However, the star seems to be at most 20 million years old, which implies that it is a

blue straggler A blue straggler is a main-sequence star in an open or globular cluster that is more luminous and bluer than stars at the main sequence turnoff point for the cluster. Blue stragglers were first discovered by Allan Sandage in 1953 while perform ...

, a star born from the merger of a

binary star system A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...

, which was earlier ejected from the center of the Milky Way. In order for this to happen, there must have originally been a three-star system, or else there were two black holes and just the two stars.

Mechanism of ejection from the Milky Way

Studies say that a triple-star system was traveling through the center of the

when it came too close to the galactic center (which is thought to have a giant

black hole A black hole is a region of spacetime where gravitation, gravity is so strong that nothing, including light or other Electromagnetic radiation, electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts t ...

). One of the stars was captured by the black hole causing the other two to be ejected from the

, where they merged to form a hot blue star. The star is moving at a speed of , about three times faster than the

's orbital velocity around the

galaxy A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. ...

's center, and also faster than the galaxy's

escape velocity In celestial mechanics, escape velocity or escape speed is the minimum speed needed for a free, non- propelled object to escape from the gravitational influence of a primary body, thus reaching an infinite distance from it. It is typically ...

. The star is about 200,000

light years A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

from the galaxy's center. Some doubt has surrounded the previous studies based on the speed and position of HE 0437-5439. The star would have to be at least 100 million years old to have traveled that distance from the galactic core, yet its mass and blue color indicate that it had burned only for 20 million years. These observations led to the explanation that it was part of a triple-star system consisting of two closely bound stars and one outer star. The black hole pulled the outer star away, which granted the star's momentum to the tight binary system and boosted both stars to escape velocity from the galaxy. As the stars traveled away, they went into normal stellar evolution, with one of them becoming a red giant and engulfing the other and forming one giant star — a blue straggler. In 2008, a team of astronomers found a match between the star's chemical composition and the characteristics of stars in the

. Support that the star originated in the LMC was strengthened because the star is only 65,000 light years away from the nearby galaxy. Later observations using the

showed that the star originated from the Milky Way's galactic center.

References

External links

HE 0437-5439 on NASATwo short video clips on the HE 0437-5439 hypervelocity star
LectureMaker film crew produces an introduction and an interview with Dr. Warren R. Brown {{DEFAULTSORT:HE 0437-5439 B-type main-sequence stars Blue stragglers Dorado (constellation) Extragalactic stars Intergalactic stars Hypervelocity stars ?

Mechanism of ejection from the Milky Way

See also

References

External links