Dwarf Galaxy or Large Globular Cluster?

February 19, 2019 - Comment

AAS Nova brings us the story of a newly found cluster of stars. However the jury’s out as as to if this group is a typical historical stellar cluster or one thing extra. The not too long ago found object FSR 1758 is the brilliant area pictured within the middle of this picture. Is that


AAS Nova brings us the story of a newly found cluster of stars. However the jury’s out as as to if this group is a typical historical stellar cluster or one thing extra.

Globular cluster or dwarf galaxy?

The not too long ago found object FSR 1758 is the brilliant area pictured within the middle of this picture. Is that this object a globular cluster or a dwarf galaxy?
Barbá et al. 2019

You would possibly suppose that we’d already found all the massive clusters of stars orbiting our galaxy. Surprisingly, there are nonetheless detections to be made — such because the not too long ago found cluster FSR 1758. However is this huge group of stars an infinite globular cluster? Or a newly detected dwarf galaxy?

A New Cluster

Zooming In

A large-field view (2.5° x 2.5°; high) and a zoomed-in view (18’ x 18’; backside) centered on FSR 1758 from the DECaPS survey.
Barbá et al. 2019

FSR 1758 was first found final 12 months, hiding within the extraordinarily dense bulge on the middle of our galaxy. Objects within the galactic bulge are very troublesome to detect: because of the excessive density of surrounding stars and dirt, not a lot of the sunshine of bulge objects makes it to us.

Based mostly on the restricted observations we initially had of FSR 1758 — and since clusters residing within the galactic bulge are sometimes anticipated to be of low mass — it was assumed that this object was a globular cluster: a spherical assortment of stars that every one shaped across the similar time from the identical cloud and are sure by their mutual gravity.

However may the issue peering into the galactic bulge imply that we’re lacking necessary particulars? One other concept posits that the a part of FSR 1758 we’re seeing is as an alternative the nucleus of a faint dwarf galaxy orbiting the Milky Manner; we merely can’t see the fainter outer reaches of the galaxy.

So which is it: globular cluster or dwarf galaxy? A workforce of scientists led by Rodolfo Barbá (College of La Serena, Chile) have gathered observations to search out out.

Revealing Particulars

Barbá and collaborators use three completely different units of observations to discover FSR 1758: optical information from Gaia’s DR2 and the DECam Aircraft Survey, and near-infrared information from the VISTA Variables within the Through Lactea Prolonged Survey. From these information, the authors decide the cluster’s place and distance, in addition to its measurement, metallicity, absolute magnitude, and correct movement.

Proper motions of stars

This plot exhibits the spatial distribution of stars which have frequent correct movement, suggesting that they belong to FSR 2758. Past the seen cluster of stars on the middle of the group, FSR 1758 seems to have a attainable bigger, prolonged construction, suggesting it might be the nucleus of a dwarf galaxy.
Barbá et al. 2019

FSR 1758 has numerous intriguing properties. If it’s a globular cluster, it’s one of many largest round our galaxy — and the half that we see might be simply the metaphorical tip of the iceberg, as a lot of its inhabitants is probably going hidden by contamination and reddening as a consequence of its location within the galactic bulge. Moreover, FSR 1758’s properties don’t match identified relationships for globular clusters, such because the correlation between measurement and metallicity.

Lastly, the authors discover further asymmetrically distributed stars additional out within the discipline with motions and colours indicating that additionally they belong to FSR 1758. These recommend that the cluster could also be extra prolonged than initially thought and might need tidal tails. These indicators assist an image wherein FSR 1758 is the nucleus of a dwarf galaxy — which the authors tentatively identify the Scorpius dwarf galaxy.

Although we nonetheless don’t have a definitive reply about FSR 1758’s nature, we will hope that future spectral information for its stars will settle the talk. And within the meantime, it’s good to be reminded that our galaxy remains to be hiding some stunning discoveries.

Quotation
“A Sequoia within the Backyard: FSR 1758—Dwarf Galaxy or Large Globular Cluster?,” Rodolfo H. Barbá et al. 2019 Astrophysical Journal Letters 870 L24. doi:10.3847/2041-8213/aaf811

This submit initially appeared on AAS Nova, which options analysis highlights from the journals of the American Astronomical Society.



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