M51-ULS-1

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
Distance28 million ly
Orbit
PrimaryM51-ULS-1 A
CompanionM51-ULS-1 B
Semi-major axis (a)50 R☉ (<3 AU)
Details
A
Mass20 M☉
Radius<25 R☉
Luminosity260,010 L☉
Temperature26,068 K
Age4-16 Myr
B
Mass1.4-10 M☉
Radius10[a]-30[b] km
Age4-16 Myr
Other designations
RX J132943+47115, IXO 79, CXOU J132943.3+471135
Database references
SIMBADdata

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 an 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.

The M51-ULS-1 planetary system[3][7]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(years) 		Eccentricity Inclination Radius
b (unconfirmed) — 45 70 — — 0.7 RJ

See also

Notes

  1. ^ Assumed radius if the secondary object is a neutron star
  2. ^ Schwarzschild radius if the secondary object is a black hole
  3. ^ 1039 erg/s = 260,010.4004 L☉
  4. ^ Applying the Stefan–Boltzmann law with a nominal solar effective temperature of 5,772 K:
    .

References

  1. ^ a b c "RX J132943+47115". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2026-01-25.
  2. ^ a b c d e f g h i "First Evidence of a Planet Identified Beyond Our Galaxy". NASA. Retrieved 2026-01-25.
  3. ^ 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.
  4. ^ 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.
  5. ^ a b c d e "Chandra Sees Evidence for Possible Planet in Another Galaxy". Chandra X-ray Observatory. Retrieved 2026-01-25.
  6. ^ 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.
  7. ^ a b "EPE Results for M51-ULS-1 b". Extrasolar Planets Encyclopaedia. Retrieved 2026-01-25.
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