M51-ULS-1
Location and artist depiction of M51-ULS-1 | ||
| Observation data Epoch J2000.0 Equinox J2000.0 | ||
|---|---|---|
| Constellation | Canes Venatici | |
| Right ascension | 13h 29m 43.31s | |
| Declination | +47° 11′ 34.8″ | |
| Apparent magnitude (V) | 24.01 | |
| Characteristics | ||
| A | ||
| Evolutionary stage | Blue supergiant | |
| Spectral type | B2-8la | |
| B | ||
| Evolutionary stage | Black hole or neutron star | |
| Astrometry | ||
| Distance | 28 million ly | |
| Orbit | ||
| Primary | M51-ULS-1 A | |
| Name | M51-ULS-1 B | |
| Semi-major axis (a) | 50 R☉ (<3 AU) | |
| Details | ||
| A | ||
| Mass | 20 M☉ | |
| Radius | <25 R☉ | |
| Luminosity | 260,010 L☉ | |
| Temperature | 26,068 K | |
| Age | 4-16 Myr | |
| B | ||
| Mass | 1.4-10 M☉ | |
| Radius | 10[a]-30[b] km | |
| Age | 4-16 Myr | |
| Other designations | ||
| RX J132943+47115, IXO 79, CXOU J132943.3+471135 | ||
| Database references | ||
| SIMBAD | data | |
M51-ULS-1, also known as RX J132943+47115, is a high-mass X-ray binary (HMXB) system in the constellation of Canes Venatici.[1][2][3] The binary system is located in the Whirlpool Galaxy, a nearby spiral galaxy some 28 million light years (or 8.6 million parsecs) away.[1][2] The binary system has an apparent visual magnitude of 24.01.[1] The binary system was discovered in 1995 in a ROSAT survey of X-ray sources in the Whirlpool Galaxy and NGC 5195.[4]
Characteristics
M51-ULS-1 is a high-mass X-ray binary system in the Whirlpool Galaxy consisting of two components, a blue supergiant, and a compact object.[2][3][5] The binary system has a predicted age between 4 and 16 million years old; it was also found that the system is probably no older than 100 million years old.[3] The compact object orbits the more massive blue supergiant star in a orbit with a semi-major axis of 50 R☉, and it was found that the semi-major axis of the binary is no larger than 3 astronomical units.[3]
The primary star, M51-ULS-1 A, is a massive, luminous early to late blue supergiant star.[2][3][6] The primary star has a spectral type of B2-8la discovered using Hubble Space Telescope photometry.[3] The primary star has a mass of about 20 M☉.[2] Because of the star's mass it is predicted that the primary star might undergo a hydrogen-poor supernovae in the future.[3] The primary star has an estimated size of <25 R☉,[3][6] based on a luminosity of ~260,000 L☉[c] and a derived effective temperature of approximately 26,000 K.[3][d]
The secondary object, M51-ULS-1 B, is a stellar remnant and is either a black hole or neutron star.[2][3][5] If the secondary object is a black hole, it would have a mass of 10 M☉; classifying the secondary object as a stellar-mass black hole.[3] If it is a black hole, using its mass it would have a Schwarzschild radius of roughly 30 kilometers.[3] If the secondary object is a neutron star, it would have mass of 1.4 M☉.[3] It is known that the secondary object is accreting 10-6 M☉ worth of material every year from the primary star.[3]
Planetary system
In September 2020, a candidate exoplanet named M51-ULS-1 b was discovered in the system using the Chandra X-ray Observatory.[2][3][5] The putative exoplanet is mainly notable for being the first extragalactic planet candidate with strong evidence.[2][3][5] The potential exoplanet was detected by the eclipses of the X-ray source (XRS);[3] i. e. M51-ULS-1 B, the compact object orbiting the primary star. The candidate exoplanet is likely slightly smaller than the planet Saturn.[3][7] The unconfirmed exoplanet orbits both of the objects in the system in about 70 years, and has a semi-major axis of 45 AU.[2][3][5] It was suggested that the planet could be a white dwarf, however this was ruled out because of the fact it would cause a lensing event and not a dip in flux.[3] It was also proposed that it may be a cloud of gas, however the discoverers found this as an unlikely explanation.[3] Due to M51-ULS-1 b orbiting a potential black hole it may be classified as a blanet.
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (years) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b (unconfirmed) | — | 45 | 70 | — | — | 0.7 RJ |
See also
- PA-99-N2, another system containing a potential extragalactic planet.
- M33 X-7, another extragalactic high-mass X-ray binary.
- Extragalactic planet
- Circumbinary planet
- Whirlpool Galaxy
Notes
- ^ Assumed radius if the secondary object is a neutron star
- ^ Schwarzschild radius if the secondary object is a black hole
- ^ 1039 erg/s = 260,010.4004 L☉
- ^ Applying the Stefan–Boltzmann law with a nominal solar effective temperature of 5,772 K:
- .
References
- ^ a b c "RX J132943+47115". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2026-01-25.
- ^ a b c d e f g h i "First Evidence of a Planet Identified Beyond Our Galaxy". NASA. Retrieved 2026-01-25.
- ^ a b c d e f g h i j k l m n o p q r s t u v Di Stefano, R. (2020). "M51-ULS-1b: The First Candidate for a Planet in an External Galaxy". NASA Ads. arXiv:2009.08987. Retrieved 2026-01-25.
- ^ Ehle, M.; Pietsch, W.; Beck, R. (1995). "ROSAT high-resolution X-ray observations of the galaxies M51 and NGC5195". Astronomy and Astrophysics. 295: 289. Bibcode:1995A&A...295..289E.
- ^ a b c d e "Chandra Sees Evidence for Possible Planet in Another Galaxy". Chandra X-ray Observatory. Retrieved 2026-01-25.
- ^ a b Terashima, Yuichi; Inoue, Hirohiko; Wilson, Andrew S. (2006). "Hubble Space Telescope Identification of the Optical Counterparts of Ultraluminous X-Ray Sources in M51". The Astrophysical Journal. 645 (1): 264. arXiv:astro-ph/0603528. Bibcode:2006ApJ...645..264T. doi:10.1086/504251.
- ^ a b "EPE Results for M51-ULS-1 b". Extrasolar Planets Encyclopaedia. Retrieved 2026-01-25.