Price-Whelan 1 (PW 1) is a young stellar association or disrupting star cluster with low metallicity and extragalactic origin, more specifically the

leading arm A (semi) trailing-arm suspension, sometimes referred to as (semi) trailing-link is a vehicle axle or wheel suspension design in which one or more horizontal arms (or "links"), perpendicular to and forward of the axle, are connecting the axle or w ...

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 bo ...

. Price-Whelan 1 was discovered by

Adrian Price-Whelan Adrian Price-Whelan is an American astronomer and researcher who is known for discovering the star cluster Price-Whelan 1. He is the son of Michael Whelan. Education Price-Whelan holds a bachelor degree in physics from New York University and ...

using Gaia data and additional cluster members were identified using DECam data. The star cluster contains less than a thousand

stars A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth ma ...

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

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

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 force to be exerted on the body. Ram pressure is given in tensor form as ...

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 galaxies comprise the halo: * the stellar halo * the galactic corona (hot gas, i.e. a plas ...

. 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 collections of gas found throughout the galactic halo of the Milky Way. Their bulk motions in the local standard of rest have velocities which are measured in excess of 70–90 km s−1. These clouds of ...

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

molecular hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, ...

, 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 {{Star-cluster-stub