Dragonfly 44

Dragonfly 44 is an ultra diffuse galaxy in the Coma Cluster.[2][3][1][4] Observations of the velocity dispersion suggest a mass of about one trillion solar masses, about the same as the mass of the Milky Way; the galaxy shows no evidence of rotation.[5] This is also consistent with about 90 globular clusters observed around Dragonfly 44. However, the galaxy emits only 1% of the light emitted by the Milky Way.[6] The galaxy was discovered with the Dragonfly Telephoto Array.[7]

Dragonfly 44
Observation data
ConstellationComa Berenices
Right ascension 13h 00m 58.0s[1]
Declination+26° 58′ 35″[1]
Redshift~0.023
Helio radial velocity6280 ± 120 km/s
Distance~100 Mpc (~330 Mly)
Group or clusterComa Cluster
Apparent magnitude (V)21 mag; or 19.4 mag [1]
Apparent magnitude (B)22
Absolute magnitude (V)-16.1 mag [1]
Characteristics
Mass~1.0×1012 M☉
Size70,000
Apparent size (V)10 x 35 arcsec
Other designations
SDSS J130057.98+265839.6, SDSS J130058.17+265836.1, SDSS J130058.21+265829.3

To determine the amount of dark matter in this galaxy, they used the DEIMOS instrument installed on Keck II to measure the velocities of stars for 33.5 hours over a period of six nights so they could determine the galaxy's mass. The scientists then used the Gemini Multi-Object Spectrograph on the 8-m Gemini North telescope to reveal a halo of spherical clusters of stars around the galaxy's core.[8]

In August 2016, astronomers reported that this galaxy might be made almost entirely of dark matter.[5][9][10]

See also

References
  1. Van Dokkum, Pieter; et al. (1 May 2015). "Spectroscopic confirmation of the existence of large, diffuse galaxies in the coma cluster". The Astrophysical Journal Letters. 804 (1): L26. arXiv:1504.03320. Bibcode:2015ApJ...804L..26V. doi:10.1088/2041-8205/804/1/L26.
  2. "Scientists discover the fluffiest galaxies". phys.org. 14 May 2015.
  3. Van Dokkum, Pieter; et al. (7 January 2015). "Forty-seven milky way-sized, extremely diffuse galaxies in the Coma-Cluster". The Astrophysical Journal Letters. 798 (2): L45. arXiv:1410.8141. Bibcode:2015ApJ...798L..45V. doi:10.1088/2041-8205/798/2/L45.
  4. Dragonfly 44: Ultra-Diffuse Galaxy Made Mostly of Dark Matter. Aug 2016
  5. Van Dokkum, Pieter; et al. (25 August 2016). "A High Stellar Velocity Dispersion and ~100 Globular Clusters For The Ultra-Diffuse Galaxy Dragonfly 44". The Astrophysical Journal Letters. 828 (1): L6. arXiv:1606.06291. Bibcode:2016ApJ...828L...6V. doi:10.3847/2041-8205/828/1/L6.
  6. Crosswell, Ken (26 July 2016). "The Milky Way's dark twin revealed". Nature News. Retrieved 30 July 2016.
  7. Rachel Feltman (25 August 2016). "A new class of galaxy has been discovered, one made almost entirely of dark matter". Washington Post.
  8. http://earthsky.org/space/dragonfly-44-dark-matter-galaxy-2016
  9. Hall, Shannon (25 August 2016). "Ghost galaxy is 99.99 per cent dark matter with almost no stars". New Scientist. Retrieved 27 August 2016.
  10. Feltman, Rachael (26 August 2016). "A new class of galaxy has been discovered, one made almost entirely of dark matter". The Washington Post. Retrieved 26 August 2016.


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