New M92 Stellar Stream Discovered

A team of astronomers using the Canada-France-Hawaii Telescope  discovered a new stellar stream emanating from the M92 globular  cluster. This new stream suggests that M92 is actively being disrupted  by tidal forces caused by our Milky Way Galaxy. This discovery  utilized high quality data obtained as part of the  Canada-France-Imaging-Survey (CFIS) using MegaCam at CFHT and from the  Pan-STARRS 1 (PS1) survey on Haleakalā, Maui. The discovery of a  stellar stream around M92 raises the question of the cluster’s origin  and could be used in the future to probe the innermost region of our  Galaxy. The team estimates that stellar stream has a mass equivalent  to ~10% of the mass of the entire M92 cluster.

Stellar streams are long thin streams of stars formed as globular  clusters or dwarf galaxies are ripped apart by the immense gravity of  the Milky Way. The structures formed by these tidal forces are stable  over many billions of years. Their longevity allows astronomers to use  their presence to better understand the formation of galaxies like the  Milky Way as a guide to determine the role of galactic cannibalism in  galaxy formation. Additionally, stellar streams are excellent tools to  probe the gravitational potential of our Galaxy and study the  distribution of dark matter around it.

“Our simulations of the M92 stellar stream indicated that the stream  was likely formed recently, in the last 500 million years,” said  Guillaume Thomas, lead author of the paper published in The  Astrophysical Journal. “The cluster’s age is around 11 billion years,  which indicates that the cluster was not always in its current orbit  and makes us wonder where M92 originally orbited.”

The team identified the 17° long stellar stream from the M92 globular  cluster stream using an improved matched-filter method. This method  aims to highlight a specific known signal in a noisy dataset and  proves to be an extremely efficient tool to detect stellar streams  around the Milky Way Galaxy.

Despite previous observations in this region, the newly discovered M92  stellar stream was hidden by the high number of foreground stars from  the Milky Way disk. It was discovered because of the combination of  high quality images from both CFIS and Pan-STARRS. The team also used  proper motions obtained by the European space mission Gaia to confirm  the existence of the stream.

The Canada-France Imaging Survey is an ongoing large program at CFHT  using MegaCam. Allocated 271 nights, CFIS aims to address some of the  most fundamental questions in astronomy including the assembly of the  Milky Way, properties of dark matter and dark energy, and the growth  of structure in the Universe from galaxies to clusters.

“The discovery of the M92 stellar stream is a testament to the power  of the CFIS/PS1 collaboration and the unique capabilities of MegaCam,”  says Todd Burdullis, queue observing specialist at the  Canada-France-Hawaii Telesope. “The CFIS program is not complete and  already the data are enhancing our understanding of the Milky Way. We  expect more discoveries like this from the CFIS team in the coming  years.”

arXiv paper link:


Guillaume Thomas
Juan de la Cierva fellow
Instituto de Astrofísica de Canarias (IAC)

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Mary Beth Laychak
Canada-France-Hawaii Telescope