|Observation data (J2000 epoch)|
|Right ascension||02h 41m 46.8s|
|Declination||−08° 24′ 12″|
|Distance (comoving)||19.0 ± 1.7 Mpc (62.0 ± 5.5 Mly)|
|Apparent size (V)||1.20′ × 1.12′|
NGC 1052-DF2 is an ultra diffuse galaxy (UDG) in the constellation Cetus, which was identified in a wide-field imaging survey of the NGC 1052 group by the Dragonfly Telephoto Array. It has been proposed that the galaxy contains little or no dark matter, the first such discovery. On 20 March 2019, a follow-up study announcing the discovery of a second UDG lacking dark matter, NGC 1052-DF4, was published.
The distance to the galaxy from Earth obtained by an international team of researchers is 22.1 +/-1.2 Mpc. Due to close proximity, it is assumed to be associated with the elliptical galaxy NGC 1052 and to lie at a distance of about 80 Kpc from NGC 1052.
On 3 June 2019, however, a separate team used a full observing dataset on the same object to review this claim, and found out that the actual distance of the galaxy was different, and that it may contain dark matter after all.
A more recent study on NGC 1052-DF2 suggests the previously reported distance of the galaxy was greatly exaggerated. Consequently, the galaxy now looks "normal" in every way. Using five independent methods to estimate distances of heavenly bodies, a team of researchers from the Instituto de Astrofísica de Canarias (IAC) found the correct distance of NGC 1052-DF2 to be 42 million light years (13 MPc), not some 64 million light years (19 MPc) from the Earth. The total mass of the galaxy is around one-half of the mass estimated previously, but the mass of its stars is only about one-quarter of the previously estimated mass. This implies a significant part of NGC 1052-DF2 could be made up of dark matter, like any other galaxies.
The apparent lack of dark matter in NGC 1052-DF2 may help prove that dark matter is real: If what appears to be dark matter is really just a currently unknown effect of the gravity of ordinary matter then this apparent dark matter should also appear in this galaxy. Further study will be needed before this and any other possible implications can be confirmed. If confirmed, the absence of dark matter may also have implications for theories of galaxy formation, as dark matter has been thought to be needed for galaxy formation.
A later study purports to show that the galaxy may contain more dark matter than initially reported. It may have a mass-to-light ratio towards the low end of expected values for a dwarf galaxy. However, a follow-up study on 20 March 2018 and a new discovery of a second ultra diffuse galaxy, NGC 1052-DF4, also apparently lacking dark matter, challenges the prior study's conclusion. In June 2021 further observations by Hubble have confirmed NGC 1052-DF2 as deficient in dark matter.
Other similar galaxies
Astronomers discovered a second Galaxy with no dark matter, NGC 1052-DF4, which is another ultra diffuse galaxy - quite large, spread-out, and faint to observe. Discovering another galaxy with very little to no dark matter means the chances of finding more of these galaxies may be higher than cosmologists previously thought.
Another group of astronomers have found the existence of tidal tails in NGC 1052-DF4 indicating that the lack of dark matter has been caused by the interaction with a nearby neighbor (a low mass disk galaxy, NGC 1035). The interaction naturally explains the low content of dark matter inferred for this galaxy and reconciles these type of galaxies with our current models of galaxy formation.
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For Mack the most exciting aspect of this galaxy is its potential to prove that dark matter - until now widely theorised but not directly observed - is real. If dark matter were just an unexplained effect of the gravity from regular matter, its effects would be visible in this galaxy. ... More work remains to be done on this and similar objects before dark matter theory needs to be fundamentally altered, however.
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We thought that every galaxy had dark matter and that dark matter is how a galaxy begins," said Pieter van Dokkum of Yale University in New Haven, Connecticut, lead researcher of the Hubble observations. "This invisible, mysterious substance is the most dominant aspect of any galaxy. So finding a galaxy without it is unexpected. It challenges the standard ideas of how we think galaxies work, and it shows that dark matter is real: It has its own separate existence apart from other components of galaxies. This result also suggests that there may be more than one way to form a galaxy.
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