Price-Whelan 1 (PW 1) is a young

stellar association A stellar association is a very loose star cluster, looser than both open clusters and globular clusters. Stellar associations will normally contain from 10 to 100 or more visible stars. An association is primarily identified by commonalities in i ...

or disrupting

star cluster A star cluster is a group of stars held together by self-gravitation. Two main types of star clusters can be distinguished: globular clusters, tight groups of ten thousand to millions of old stars which are gravitationally bound; and open cluster ...

with low

metallicity In astronomy, metallicity is the Abundance of the chemical elements, abundance of Chemical element, elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-Dark matter, dark) matt ...

and extragalactic origin, more specifically the

leading arm A trailing-arm suspension, also referred to as trailing-link, is a form of vehicle suspension. In a motor vehicle it places one or more horizontal arms (or "links") perpendicular to and forward of the axle on the chassis or unibody, which are c ...

of the Magellanic gas stream originating in the

Magellanic Clouds The Magellanic Clouds (''Magellanic system'' or ''Nubeculae Magellani'') are two irregular dwarf galaxies in the southern celestial hemisphere. Orbiting the Milky Way galaxy, these satellite galaxies are members of the Local Group. Because both ...

. Price-Whelan 1 was discovered by Adrian Price-Whelan using

Gaia In Greek mythology, Gaia (; , a poetic form of ('), meaning 'land' or 'earth'),, , . also spelled Gaea (), is the personification of Earth. Gaia is the ancestral mother—sometimes parthenogenic—of all life. She is the mother of Uranus (S ...

data and additional cluster members were identified using

DECam The Dark Energy Survey (DES) is an astronomical survey designed to constrain the properties of dark energy. It uses images taken in the near-ultraviolet, visible, and near-infrared to measure the expansion of the universe using Type Ia supernov ...

data. The star cluster contains less than a thousand

stars A star is a luminous spheroid of plasma held together by self-gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night; their immense distances from Earth make them appear as fixed points of ...

. The existence of Price-Whelan 1 suggests that the stream of gas extending from the Magellanic Clouds to our

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

is about half as far from the Milky Way as previously thought.

Structure

The star cluster has larger component 'a' and a smaller component 'b'. The component 'a' was later resolved in two components: an Eastern component 'aE' and a Western component 'aW'. The three components do not only differ in position, but also in stellar content.

The parent gas cloud of PW 1

Price-Whelan 1 is about ten degrees offset from the leading arm II. This difference is explained with the gas experiencing

ram pressure Ram pressure is a pressure exerted on a body moving through a fluid medium, caused by relative bulk motion of the fluid rather than random thermal motion. It causes a drag (physics), drag force to be exerted on the body. Ram pressure is given in ...

as it passes through the hot gas of the

Milky Way halo A galactic halo is an extended, roughly spherical component of a galaxy which extends beyond the main, visible component. Several distinct components of a galaxy comprise its halo: * the stellar halo * the galactic corona (hot gas, i.e. a plasma) ...

. The stars will not feel this force. Over time the gas and the stars will decouple, resulting in a different position and velocity for both components. Another possible origin of the star cluster could be the

high-velocity cloud High-velocity clouds (HVCs) are large accumulations of gas with an unusually rapid motion relative to their surroundings. They can be found throughout the galactic halo of the Milky Way. Their bulk motions in the local standard of rest have veloc ...

HVC 287.5+22.5+240, which has a similar metallicity compared with Price-Whelan 1. This cloud is part of the leading arm and displays a strong

magnetic field A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...

, which could stabilize the cloud against the ram pressure. The cloud also shows traces of

molecular hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

, which can also be found in star-forming regions.

References

External links

Discovery of a new star cluster: Price-Whelan 1
"Image of the Week" at ESA Gaia
The Milky Way’s Impending Galactic Collision Is Already Birthing New Stars
Simons Foundation Open clusters Hydra (constellation) {{Star-cluster-stub