MGC1

Lore & Background

MGC1 is a globular cluster in the constellation of Pisces, situated about 650,000 light-years (200 kpc) from the center of the Andromeda Galaxy (M31). Its radial velocity is close to the systemic velocity of M31 and likely within its escape velocity, indicating the cluster is probably gravitationally bound to that galaxy. It is considered one of the most isolated globular clusters in the Local Group.

In 2010, three astronomers—Charlie Conroy, Abraham Loeb, and David Spergel—submitted an article to The Astrophysical Journal explaining with evidence that MGC1 and another globular cluster, NGC 2419, did not have dark matter halos surrounding them. A separate article submitted to Science Magazine described how the team used data obtained by other astronomers to create computer models of globular clusters with and without dark matter halos. Over time, clusters without dark matter slowly lose their gravitational grip on stars at their edges, whereas those with halos hold onto these stars. Both NGC 2419 and MGC1 are missing stars at their fringes, leading the researchers to conclude that they formed in the absence of dark matter halos.

Reader's Guide

The significance of MGC1 lies in its role in challenging the prior belief that dark matter helped form all globular clusters. The 2010 research by Conroy, Loeb, and Spergel, submitted to The Astrophysical Journal, provided evidence that MGC1 and NGC 2419 lack dark matter halos. A subsequent article in Science Magazine explained that computer models showed clusters without dark matter halos lose stars at their edges over time, while those with halos retain them. The observation that both MGC1 and NGC 2419 are missing stars at their fringes led to the conclusion that they formed without dark matter halos. This finding suggests that the same may be true of most globular clusters in the local universe, thereby disproving the earlier assumption that dark matter was necessary for the formation of all globular clusters. MGC1 thus serves as a key example in the ongoing understanding of globular cluster formation and the role of dark matter.

Did You Know?

• Its absolute magnitude is −8.5.
• Research submitted in 2010 indicated that MGC1 lacks a dark matter halo.