Seeking the Origins of Galactic Stellar Streams

Photo of an edge-on galaxy encircled by a faint stream of stars.
Like NGC 5907, the edge-on galaxy proven right here, our personal Milky Way hosts faint streams of stars that loop round it. But the place did these streams originate?
R. Jay GaBany

The Milky Way is enwreathed in lengthy streams of stars that maintain clues to every little thing from our galaxy’s historical past to the nature of darkish matter. New analysis has now recognized the doubtless origins of some of these delicate ribbons.

Streams Across the Sky

A graph showing the orbital energy vs. angular momentum of the stars in 23 of the Milky Way’s stellar streams, as compared to field stars.
The orbital power vs. angular momentum of the stars in 23 of the Milky Way’s stellar streams (coloured and labeled information), as in comparison with area stars (black information).
Bonaca et al. 2021

Stellar streams are associations of stars which can be grouped into elongated filaments arcing round a bunch galaxy. These filaments are considered produced when a stream progenitor — like a globular cluster or a satellite tv for pc dwarf galaxy — is disrupted by its host galaxy’s tidal forces. Stars are drawn out from the progenitor right into a tidal stream that then orbits the host galaxy; the progenitor itself could stay linked to the stream, orbit individually, or disrupt totally.

We’ve noticed stellar streams in different galaxies (like NGC 5907, proven above), however we needn’t look that distant — our personal Milky Way is host to greater than 60 catalogued streams. Of these skinny trails, solely a handful have been linked to a identified progenitor, like a surviving globular cluster. The relaxation have unknown origins, leaving a quantity of open questions that solely now, with present observations, have solutions inside attain.

In a current research led by Ana Bonaca (Center for Astrophysics | Harvard & Smithsonian), a workforce of scientists has leveraged the unimaginable precision of the Gaia space observatory to hunt for the origins of 23 chilly stellar streams in the Milky Way halo.

A Disrupted Home

A graph showing the locations in orbital phase space of the 23 stellar streams.
Locations in orbital section space of the 23 stellar streams, labeled by whether or not they have a dwarf galaxy progenitor (pentagon) or globular cluster progenitor (star). Only one stream, Svöl, falls into the area related to doable in situ formation (relatively than having been introduced in by way of a dwarf galaxy).
Adapted from Bonaca et al. 2021

Bonaca and collaborators make use of improved correct motions supplied in Gaia’s Early Data Release 3 for stars in these 23 streams. By analyzing the energies and 3D angular momenta of these streams, and by inspecting how the streams are distributed in bodily space, the authors are in a position to determine the possible progenitors for many of the streams.

According to the authors’ outcomes, only one of the streams plausibly originated from a globular cluster that was born in the Milky Way. The overwhelming majority as an alternative originated from dwarf galaxies that the Milky Way has accreted. Some of the streams have been produced from the dwarf galaxies themselves; others have been doubtless fashioned from disrupted globular clusters that orbited these dwarf galaxies.

Several of the 23 streams have comparable properties, suggesting that many originated from the similar progenitors. The authors determine authentic host dwarf galaxy candidates for 20 of the streams, they usually level to six particular globular clusters as the origin of 8 of the streams.

Illuminating Dark Matter

A sky map showing the 6 globular clusters that the authors associate with 8 stellar streams.
Sky map exhibiting the 6 globular clusters (crosses) that the authors affiliate with 8 stellar streams (circles).
Adapted from Bonaca et al. 2021

What can we do with this data? Understanding the origin of these stellar streams permits us to raised hint their paths, how lengthy they’ve been orbiting, and what different gravitational interactions they might have had over time. These particulars are beneficial not only for understanding galaxy evolution, but additionally for mapping out the big-picture distribution of darkish matter in our galaxy and learning the small-scale construction of darkish matter in the streams’ host galaxies.

Further enlargement of Bonaca and collaborators’ work to the different stellar streams orbiting the Milky Way will depend on continued high-quality correct movement measurements of these faint and distant sources. Look for extra outcomes as future Gaia information is launched!


“Orbital Clustering Identifies the Origins of Galactic Stellar Streams,” Ana Bonaca et al 2021 ApJL 909 L26. doi:10.3847/2041-8213/abeaa9

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


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