View source for Astronomy:RX J0806.3+1527

{{Short description|Binary star in the constellation Cancer}}
{{Starbox begin |
 name=RX J0806.3+1527 }}
{{Starbox image |
 image=[[File:J0806 (binary star - artist's conception).jpg|250px]] |
 caption=An artist's depiction of J0806. }}
{{Starbox observe |
 epoch=J2000 |
 constell=[[Astronomy:Cancer (constellation)|Cancer]] |
 ra={{RA|08|06|22.95196}}<ref name=GaiaDR2>{{cite DR2|654879021108862464}}</ref> |
 dec={{DEC|+15|27|31.0073}}<ref name=GaiaDR2/> |
 appmag_v= }}
|- style="vertical-align: top;"
| '''[[Astronomy:Cosmic distance ladder|Distance]] '''
| 1,600 [[Astronomy:Light-year|Light-year]]s
|-
! style="background-color: #FFFFC0;" colspan="2" | [[Astronomy:Binary star|Binary orbit]]
|- style="vertical-align: top;"
| '''[[Astronomy:Orbital period|Period]] <small>(P)</small>'''
| 321.5 seconds
|- style="vertical-align: top;"
| '''dP/dt <small>(Pdot)</small>'''
| 1.1 milliseconds per year
|- style="vertical-align: top;"
| '''Separation:'''
| 0.0005 [[Astronomy:Astronomical unit|AU]]
{{Starbox detail |
 mass=0.5 (primary) / 0.5 (b) |
 radius= |
 temperature=
}}
{{Starbox catalog
| names = RX J0806.3+1527, RX J0806, J0806, HM Cancri, HM Cnc
}}
{{Starbox reference
| Simbad = HM+Cnc
}}
{{Starbox end}}

'''RX J0806.3+1527''' or '''HM Cancri''' (sometimes shortened to ''HM Cnc'' or ''J0806'' after establishing identity) is an [[Astronomy:X-ray binary|X-ray binary]] star system about {{convert|1600|ly|pc+km}} away.<ref>{{cite web
 |url          = http://chandra.harvard.edu/
 |title        = RX J0806.3+1527: Orbiting Stars Flooding Space with Gravitational Waves
 |date         = 2005-05-30
 |publisher    = CHANDRA X-RAY OBSERVATORY, Harvard
 |archive-url  = https://web.archive.org/web/20110225085358/http://chandra.harvard.edu/
 |archive-date = 2011-02-25
 |access-date  = 2013-05-31
 |url-status   = bot: unknown
}}</ref> It comprises two dense [[Astronomy:White dwarf|white dwarf]]s orbiting each other once every 321.5&nbsp;seconds (in this system the "year" duration is of only 5.4 minutes), at an estimated distance of only {{convert|80000|km|miles}} apart (about 1/5 the distance between the Earth and the Moon). The two stars orbit each other at speeds in excess of {{convert|400|km/s|mph}}. The stars are estimated to be about half as massive as the [[Astronomy:Sun|Sun]]. Like typical white dwarfs, they are extremely dense, being composed of degenerate matter, and so have radii on the order of the Earth's radius. Astronomers believe that the two stars will eventually merge, based on data from many X-ray satellites, such as  Chandra X-Ray Observatory, [[Astronomy:XMM-Newton|XMM-Newton]] and the Swift Gamma-Ray Burst Mission. These data show that the orbital period of the two stars is steadily decreasing at a rate of 1.2&nbsp;milliseconds per year as they thus are getting closer by approximately {{convert|60|cm|ft}} per day. At this rate, they can be expected to merge in approximately 340,000 years. With a revolution period of 5.4 minutes, RX J0806.3+1527 is the shortest orbital period binary white dwarf system currently known.

==Observations==
[[File:HMCncLightCurve.png|thumb|left|A green band light curve for HM Cancri, adapted from Barros ''et al.'' (2007)<ref name="Barros">{{cite journal |last1=Barros |first1=S. C. C. |last2=Marsh |first2=T. R. |last3=Dhillon |first3=V. S. |last4=Groot |first4=P. J. |last5=Littlefair |first5=S. |last6=Nelemans |first6=G. |last7=Roelofs |first7=G. |last8=Steeghs |first8=D. |last9=Wheatley |first9=P. J. |title=ULTRACAM photometry of the ultracompact binaries V407 Vul and HM Cnc |journal=Monthly Notices of the Royal Astronomical Society |date=1 February 2007 |volume=374 |issue=4 |pages=1334–1346 |doi=10.1111/j.1365-2966.2006.11244.x |s2cid=15741292 |url=https://doi.org/10.1111/j.1365-2966.2006.11244.x |access-date=12 November 2021}}</ref>]]
As RX J0806.3+1527 is a pair of white dwarfs, it has a relatively low optical luminosity. The 321.5&nbsp;s modulation of RX J0806.3+1527 was discovered serendipitously in 1999 thanks to the [[Astronomy:ROSAT|ROSAT]] mission  working in the X-ray band. Optical follow-up observations with the ESO  [[Astronomy:Very Large Telescope|Very Large Telescope]] (VLT), Telescopio Nazionale Galileo (TNG) and [[Astronomy:Nordic Optical Telescope|Nordic Optical Telescope]] (NOT) allowed the counterpart to be identified, a relatively dim (20.7 [[Astronomy:Magnitude|magnitude]] in the B filter) object which shows an optical modulation at the same period detected in the X-ray band. The optical monitoring of the counterpart of RX J0806.3+1527 during 2001-2004 clearly shows that the period is decreasing at a rate of about 1/1000&nbsp;s each year. This result was confirmed by monitoring the source in the X-rays for several years.

==Relation to general relativity==
The decreasing separation of the components of the system mean that the system is losing orbital energy.  [[Biography:Albert Einstein|Albert Einstein]]'s theory of General Relativity predicts such a system will lose orbital energy through the generation of gravitational waves. Scientists believe that RX J0806.3+1527 may be one of the strongest sources of gravitational waves in the Milky Way galaxy.{{Citation needed|date=December 2013}}

==Sources==
{{Reflist}}
* {{APOD |date=1 June 2005 |title=White Dwarf Star Spiral}}
* [http://www.nasa.gov/centers/marshall/news/news/releases/2005/05-078.html NASA Sees Orbiting Stars Flooding Space With Gravitational Waves]
* [http://chandra.harvard.edu/photo/2005/j0806/ RX J0806.3+1527: Orbiting Stars Flooding Space with Gravitational Waves]

==Further reading==
* [https://www.science.org/doi/full/10.1126/science.295.5562.1997 Science Journal: News of the Week]
* [http://www.eso.org/public/news/eso0211/ European southern Observatory Press Release]
* [https://academic.oup.com/mnras/article/332/1/L7/975156 RX J0806115: the shortest period binary?]
* [http://www.aanda.org/articles/aa/abs/2014/01/aa22719-13/aa22719-13.html Simultaneous X-ray UV observations of HM Cnc]
* [http://iopscience.iop.org/2041-8205/711/2/L138/ Doppler tomography of RXJ0806]
* [https://arxiv.org/abs/1003.1986 Phase Resolved Optical spectroscopy of RXJ0806]
* [http://www.aanda.org/index.php?option=com_article&access=bibcode&Itemid=129&bibcode=2007A%2526A...464..417DFUL RXJ0806 and the unipolar inductor model]
* [http://sait.oat.ts.astro.it/MSAIS/5/PDF/148.pdf Coherent timing solution for RXJ0806]
* [http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1999A%26A...349L...1I&amp;data_type=PDF_HIGH&amp;whole_paper=YES&amp;type=PRINTER&amp;filetype=.pdf Discovery of the 321.5s modulation in RXJ0806]
* [http://www.aanda.org/index.php?option=com_article&access=bibcode&Itemid=129&bibcode=2002A%2526A...386L..13IFUL Spectroscopic optical study of RXJ0806]
* [http://www.mssl.ucl.ac.uk/www_astro/preprints/gtbr/rx0806_3.pdf.gz Monitoring the spin up in RX J0806+15]
* [http://www.journals.uchicago.edu/ApJ/journal/issues/ApJL/v593n1/17440/17440.html Phase Coherent Timing of RX J0806.3+1527 with ROSAT and Chandra]
* [http://jumk.de/astronomie/special-stars/rx-j0806.shtml RX J0806]
* [https://www.youtube.com/watch?v=ryqN6dyUmJg RX J0806.3+1527 Gravitational Wave Merger]
* [https://arxiv.org/abs/1003.0658v1 SPECTROSCOPIC EVIDENCE FOR A 5.4-MINUTE ORBITAL PERIOD IN HM CANCRI]

{{Stars of Cancer}}

{{DEFAULTSORT:RX J0806.3+1527}}
[[Category:Cancer (constellation)]]
[[Category:Objects with variable star designations|Cancri, HM]]
[[Category:ROSAT objects]]
[[Category:X-ray binaries]]
[[Category:White dwarfs]]

{{Sourceattribution|RX J0806.3+1527|1}}