HE 0437-5439
Encyclopedia
HE 0437-5439 is a massive, unbound hypervelocity star (HVS), also called HVS3. It is a main sequence
B-type
star
located in the Dorado constellation. It was discovered in 2005 with the Kueyen 8.2 meter telescope, which is part of the European Southern Observatory
's Very Large Telescope
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
and the star is located 200,000 light years away in the direction of the Dorado
constellation, 16 degrees northwest of the Large Magellanic Cloud
(LMC) and further away than the LMC. The star appears to be receding at an extremely high velocity of 723 km/s, or 2600000 kilometres per hour (1,615,565.1 mph). At this speed, the star is no longer gravitationally bound and will leave the Milky Way
galaxy system and escape into intergalactic space. 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
in the LMC.
In 2010 a study was published in which its proper motion
was estimated using images from the Hubble Space Telescope
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 Milky Way
. 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 star born from the merger of a binary star system, 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.
when it made a misstep by wandering too close to the galactic center (which is thought to have a giant black hole
). One of the stars was captured by the black hole and thus the other two were pushed out of the Milky Way
, where they merged to form a hot blue star. The baby star is blazing across space at a speed of 1600000 mi/h, about three times faster than our Sun
's orbital velocity around the galaxy
's center. This is enough speed to escape the galaxy's gravitational force.
The stellar outcast is about 200,000 light years
from the center now. 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, which 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, boosting both stars to escape velocity from the galaxy. And as they traveled away they went into normal stellar evolution, with one of them becoming a red giant and engulfing the other, forming one superstar - a blue straggler.
In 2008 a team of astronomers found match between the star's chemical composition and the characteristics of stars in the Large Magellanic Cloud
. Support that the star originated in the LMC is strengthened since the star is only 65,000 light-years away from the nearby galaxy.
Main sequence
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 Hertzsprung and Henry Norris Russell...
B-type
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
located in the Dorado constellation. It was discovered in 2005 with the Kueyen 8.2 meter telescope, which is part of the European Southern Observatory
European Southern Observatory
The European Southern Observatory is an intergovernmental research organisation for astronomy, supported by fifteen countries...
's Very Large Telescope
Very Large Telescope
The Very Large Telescope is a telescope operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. The VLT consists of four individual telescopes, each with a primary mirror 8.2m across, which are generally used separately but can be used together to...
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
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
and the star is located 200,000 light years away in the direction of the Dorado
Dorado
Dorado is a constellation in the southern sky. It was created in the late 16th century and is now one of the 88 modern constellations. Its name refers to the dolphinfish , which is known as dorado in Spanish, although it has also been depicted as a swordfish...
constellation, 16 degrees northwest of the Large Magellanic Cloud
Large Magellanic Cloud
The Large Magellanic Cloud is a nearby irregular galaxy, and is a satellite of the Milky Way. At a distance of slightly less than 50 kiloparsecs , the LMC is the third closest galaxy to the Milky Way, with the Sagittarius Dwarf Spheroidal and Canis Major Dwarf Galaxy lying closer to the center...
(LMC) and further away than the LMC. The star appears to be receding at an extremely high velocity of 723 km/s, or 2600000 kilometres per hour (1,615,565.1 mph). At this speed, the star is no longer gravitationally bound and will leave the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
galaxy system and escape into intergalactic space. 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
Supermassive black hole
A supermassive black hole is the largest type of black hole in a galaxy, in the order of hundreds of thousands to billions of solar masses. Most, and possibly all galaxies, including the Milky Way, are believed to contain supermassive black holes at their centers.Supermassive black holes have...
in the LMC.
In 2010 a study was published in which its proper motion
Proper motion
The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
was estimated using images from the Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
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 Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
. 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
Blue straggler
Blue stragglers are main sequence stars in open or globular clusters that are more luminous and bluer than stars at the main sequence turn-off point for the cluster. Blue stragglers were first discovered by Allan Sandage in 1953 while performing photometry of the stars in the globular cluster M3...
, a star born from the merger of a binary star system, 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 Milky WayMilky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
when it made a misstep by wandering too close to the galactic center (which is thought to have a giant black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
). One of the stars was captured by the black hole and thus the other two were pushed out of the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
, where they merged to form a hot blue star. The baby star is blazing across space at a speed of 1600000 mi/h, about three times faster than our Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
's orbital velocity around the galaxy
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
's center. This is enough speed to escape the galaxy's gravitational force.
The stellar outcast is about 200,000 light years
Light Years
Light Years is the seventh studio album by Australian recording artist Kylie Minogue. It was released on 25 September 2000 by Parlophone and Mushroom Records. The album's style was indicative of her return to "mainstream pop dance tunes"....
from the center now. 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, which 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, boosting both stars to escape velocity from the galaxy. And as they traveled away they went into normal stellar evolution, with one of them becoming a red giant and engulfing the other, forming one superstar - a blue straggler.
In 2008 a team of astronomers found match between the star's chemical composition and the characteristics of stars in the Large Magellanic Cloud
Large Magellanic Cloud
The Large Magellanic Cloud is a nearby irregular galaxy, and is a satellite of the Milky Way. At a distance of slightly less than 50 kiloparsecs , the LMC is the third closest galaxy to the Milky Way, with the Sagittarius Dwarf Spheroidal and Canis Major Dwarf Galaxy lying closer to the center...
. Support that the star originated in the LMC is strengthened since the star is only 65,000 light-years away from the nearby galaxy.
External Links
- HE 0437-5439 on NASA
- Two short video clips on the HE 0437-5439 hypervelocity star LectureMaker film crew produces an introduction and an interview with Dr. Warren R. Brown