HM Cancri

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title: "HM Cancri" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["cancer-(constellation)", "objects-with-variable-star-designations", "rosat-objects", "x-ray-binaries", "white-dwarfs"] description: "Binary star in the constellation Cancer" topic_path: "general/cancer-constellation" source: "https://en.wikipedia.org/wiki/HM_Cancri" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Binary star in the constellation Cancer ::

name=HM Cancri }} image=[[File:J0806 (binary star - artist's conception).jpg|250px]] | caption=An artist's depiction of J0806. }} epoch=J2000 | constell=Cancer | ra= | dec= | appmag_v= }} |- style="vertical-align: top;" | **Distance **

1,600 Light-years
! style="background-color: #FFFFC0;" colspan="2"
- style="vertical-align: top;"
Period (P)
321.5 seconds
- style="vertical-align: top;"
dP/dt (Pdot)
1.1 milliseconds per year
- style="vertical-align: top;"
Separation:
0.0005 AU
mass=0.5 (primary) / 0.5 (b)
radius=
temperature=
names = RX J0806.3+1527, RX J0806, J0806, HM Cancri, HM Cnc
Simbad = HM+Cnc

HM Cancri (also known as HM Cnc or RX J0806.3+1527) is a binary star system about 1600 ly away.{{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

Observations

::figure[src="https://upload.wikimedia.org/wikipedia/commons/d/d8/HMCncLightCurve.png" caption="bibcode=2007MNRAS.374.1334B }}"] ::

As HM Cancri is a pair of white dwarfs, it has a relatively low optical luminosity. The 321.5 s modulation of HM Cancri was discovered serendipitously in 1999 thanks to the ROSAT mission working in the X-ray band. Optical follow-up observations with the ESO Very Large Telescope (VLT), Telescopio Nazionale Galileo (TNG) and Nordic Optical Telescope (NOT) allowed the counterpart to be identified, a relatively dim (20.7 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 HM Cancri during 2001-2004 clearly shows that the period is decreasing at a rate of about 1/1000 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. Albert Einstein's theory of General Relativity predicts such a system will lose orbital energy through the generation of gravitational waves. Scientists believe that HM Cancri may be one of the strongest sources of gravitational waves in the Milky Way galaxy.

Sources

• RX J0806.3+1527: Orbiting Stars Flooding Space with Gravitational Waves

References

1. {{cite DR2. 654879021108862464
2. (1 February 2007). "ULTRACAM photometry of the ultracompact binaries V407 Vul and HM Cnc". Monthly Notices of the Royal Astronomical Society.
3. link. "NASA Sees Orbiting Stars Flooding Space with Gravitational Waves". (2005-05-30). CHANDRA X-RAY OBSERVATORY, Harvard
4. (2010). "Spectroscopic Evidence for a 5.4 Minute Orbital Period in HM Cancri". The Astrophysical Journal.

::callout[type=info title="Wikipedia Source"] This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page. ::