View source for Astronomy:HE 0437-5439

{{Short description|Hypervelocity star in the constellation Dorado}}
{{Starbox begin |
 name=HE 0437-5439 }}
{{Starbox image 
| image = [[Image:HE 0437-5439 HST.jpg|250px]]
| caption = 
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{{Starbox observe
| epoch=[[Astronomy:J2000.0|J2000.0]] ([[Astronomy:International Celestial Reference System|ICRS]])
| constell=Dorado
| ra={{RA|04|38|12.772}}<ref name="aa"/>
| dec={{DEC|-54|33|11.86}}
| appmag_v=16.42
}}
{{Starbox character
| class=BV or sdB+F
}}
{{Starbox astrometry
| dist_ly=200,000
}}
{{Starbox detail
| mass=8
| age_myr=25 }}
{{Starbox catalog
| names=GSC2 S01132011256, HE 0437-5439, [BGK2006] HV 3, HVS3. }}
{{Starbox reference |
  Simbad=HE0437-5439 }}
{{Starbox end}}

'''HE 0437-5439''' is a massive, unbound [[Astronomy:Hypervelocity star|hypervelocity star]] (HVS), also called '''HVS3'''.<ref name=Brown/> It is a [[Astronomy:Main sequence|main sequence]] [[Astronomy:Stellar classification|B-type]] [[Astronomy:Star|star]] located in the Dorado constellation. It was discovered in 2005 with the Kueyen {{convert|8.2|m|inch|adj=on}} telescope, which is part of the [[Organization:European Southern Observatory|European Southern Observatory]]'s [[Astronomy:Very Large Telescope|Very Large Telescope]] array. HE 0437-5439 is a young star, with an age of around 30 million years.<ref name = "ESO051109"/> The mass of the star is almost nine times greater than the mass of the [[Astronomy:Sun|Sun]]<ref name="Sciencedaily"/> and the star is located 200,000 light years away in the direction of the [[Astronomy:Dorado|Dorado]] constellation, 16 degrees northwest of the [[Astronomy:Large Magellanic Cloud|Large Magellanic Cloud]] (LMC) and farther away than the LMC.<ref name = "ESO051109"/> The star appears to be receding at an extremely high velocity of {{Convert|723|km/s}}, or {{Convert|2600000|km/h}}. At this speed, the star is no longer [[Physics:Gravity|gravitationally]] bound and will leave the [[Astronomy:Milky Way|Milky Way]] galaxy system and escape into [[Astronomy:Intergalactic space|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 [[Astronomy:Supermassive black hole|supermassive black hole]] in the LMC.<ref name="Sciencedaily"/>

In 2010 a study was published in which its [[Astronomy:Proper motion|proper motion]] was estimated using images from the [[Astronomy:Hubble Space Telescope|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 [[Astronomy:Milky Way|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 [[Astronomy:Blue straggler|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.<ref name=Brown/>

== Mechanism of ejection from the Milky Way ==
Studies say that a triple-star system was traveling through the center of the [[Astronomy:Milky Way|Milky Way]] when it came too close to the [[Galactic Center]] (which is thought to have a giant [[Astronomy:Black hole|black hole]]). One of the stars was captured by the black hole causing the other two to be ejected from the [[Astronomy:Milky Way|Milky Way]], where they merged to form a hot blue star. The star is moving at a speed of {{Convert|1600000|mi/h}}, about three times faster than the [[Astronomy:Sun|Sun]]'s orbital velocity around the [[Astronomy:Galaxy|galaxy]]'s center, and also faster than the galaxy's [[Astronomy:Escape velocity|escape velocity]].

The star is about 200,000 light years 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 &mdash; 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 [[Astronomy:Large Magellanic Cloud|Large Magellanic Cloud]]. Support that the star originated in the LMC was strengthened because the star is only 65,000 light years away from the nearby galaxy.<ref>{{cite journal| doi =10.1111/j.1745-3933.2007.00280.x| title =A hypervelocity star from the Large Magellanic Cloud| date =2007| last1 =Gualandris| first1 =A.| last2 =Portegies Zwart| first2 =S.| journal =Monthly Notices of the Royal Astronomical Society: Letters| volume =376| issue =1| pages =L29–L33|arxiv = astro-ph/0612673 |bibcode = 2007MNRAS.376L..29G | s2cid =2992585}}</ref><ref>{{cite journal| doi =10.1051/0004-6361:200809391| title =LMC origin of the hyper-velocity star HE 0437-5439| date =2008| last1 =Przybilla| first1 =N.| last2 =Nieva| first2 =M. F.| last3 =Heber| first3 =U.| last4 =Firnstein| first4 =M.| last5 =Butler| first5 =K.| last6 =Napiwotzki| first6 =R.| last7 =Edelmann| first7 =H.| journal =Astronomy and Astrophysics| volume =480| issue =3| pages =L37|arxiv = 0801.4456 |bibcode = 2008A&A...480L..37P | s2cid =17157851}}</ref> Later observations using the [[Astronomy:Hubble Space Telescope|Hubble Space Telescope]] showed that the star originated from the Milky Way's galactic center.<ref name=Brown/>

{{multiple image
| align = center
| image1 = HE 0437-5439 mechanism.jpg
| width1 = {{#expr: (300 * (2400 / 1800)) round 0}}
| alt1 = 
| caption1 = Illustration of the proposed mechanism of ejection.
| image2 = HE_0437-5439_location.jpg
| width2 = {{#expr: (300 * (2346 / 3000)) round 0}}
| alt2 = 
| caption2 = Exact position of the star.
| footer = 
}}

== See also ==
*Intergalactic stars
*[[Astronomy:Stellar kinematics|Stellar kinematics]]
*[[Astronomy:Blue straggler|Blue straggler]]

== References ==
{{reflist|refs=

<ref name="aa">[http://adsabs.harvard.edu/abs/2003AcA....53..133U The Optical Gravitational Lensing Experiment. Additional Planetary and Low-Luminosity Object Transits from the OGLE 2001 and 2002 Observational Campaigns], A. Udalski, G. Pietrzynski, M. Szymanski, M. Kubiak, K. Zebrun, I. Soszynski, O. Szewczyk, and L. Wyrzykowski, ''Acta Astronomica'' '''53''' (June 2003), pp. 133–149.</ref>

<ref name = "ESO051109">{{cite press release|title = Star on the Run - Speeding Star Observed with VLT Hints at Massive Black Hole|publisher = [[Organization:European Southern Observatory|European Southern Observatory]]|date = November 9, 2005|url = http://www.ESO.Org/public/news/eso0536/|accessdate = January 28, 2008}}</ref>

<ref name="Sciencedaily">{{cite news|title = Hyperfast Star Proven To Be Alien|work = Space & Time|publisher = Science Daily|date = January 28, 2008|url = https://www.sciencedaily.com/releases/2008/01/080128113256.htm|accessdate = January 28, 2008}}</ref>

<ref name=Brown>{{Cite journal|title=A Galactic Origin For HE 0437–5439, The Hypervelocity Star Near The Large Magellanic Cloud|first1=Warren R.|last1=Brown|first2=Jay|last2=Anderson|first3=Oleg Y.|last3=Gnedin|first4=Howard E.|last4=Bond|first5=Margaret J.|last5=Geller|first6=Scott J.|last6=Kenyon|first7=Mario|last7=Livio|journal=The Astrophysical Journal Letters|date=July 19, 2010|doi=10.1088/2041-8205/719/1/L23|volume=719|issue=1|pages=L23–L27|arxiv = 1007.3493 |bibcode = 2010ApJ...719L..23B |s2cid=55832434}}</ref>
}}

==External links==
*[http://www.nasa.gov/mission_pages/hubble/science/expelled-star.html HE 0437-5439 on NASA]
*[http://www.lecturemaker.com/2010/09/hot-star-leaves-dance/ 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

{{Stars of Dorado}}

{{DEFAULTSORT:HE 0437-5439}}
[[Category:B-type main-sequence stars]]
[[Category:Extragalactic stars]]
[[Category:Hypervelocity stars]]

{{Sourceattribution|HE 0437-5439}}