| Price-Whelan 1 | |
|---|---|
| Observation data (J2000 epoch) | |
| Constellation | Hydra |
| Right ascension | 11h 55m 12s [1] |
| Declination | −29° 23′ 00″ [1] |
| Distance | 94200 [1] (28.9±0.1 kpc [1] ) |
| Physical characteristics | |
| Mass | 1200 [1] M☉ |
| Estimated age | 130±6 Myr [1] |
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 of the Magellanic gas stream originating in the Magellanic Clouds. Price-Whelan 1 was discovered by Adrian Price-Whelan using Gaia data and additional cluster members were identified using DECam data. The star cluster contains less than a thousand stars. The existence of Price-Whelan 1 suggests that the stream of gas extending from the Magellanic Clouds to our Milky Way is about half as far from the Milky Way as previously thought. [2] [1]
The star cluster has larger component 'a' and a smaller component 'b'. [1] 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. [3]
Price-Whelan 1 is about ten degrees offset from the leading arm II. This difference is explained with the gas experiencing ram pressure as it passes through the hot gas of the Milky Way halo. 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. [4] Another possible origin of the star cluster could be the high-velocity cloud 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, which can also be found in star-forming regions. [3]
The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have generated the variety of structures observed in nearby galaxies. Galaxy formation is hypothesized to occur from structure formation theories, as a result of tiny quantum fluctuations in the aftermath of the Big Bang. The simplest model in general agreement with observed phenomena is the Lambda-CDM model—that is, that clustering and merging allows galaxies to accumulate mass, determining both their shape and structure.
The Local Group is the galaxy group that includes the Milky Way. It has a total diameter of roughly 3 Mpc (or 10 Mly ≈ 1023 m), and a total mass of the order of 2×1012 solar masses (4×1042 kg). It consists of two clusters of galaxies in a "dumbbell" shape, the Milky Way and its satellites on one hand, and the Andromeda Galaxy and its satellites on the other. The two clusters are separated by about 0.8 Mpc and move towards one another with a velocity of 123 km/s. The group itself is a part of the larger Virgo Supercluster, which may be a part of the Laniakea Supercluster. The total number of galaxies in the Local Group is unknown (due to its partial occlusion by the Milky Way) but known to exceed 54, most of them being dwarf galaxies.
Star clusters are very large groups of stars. Two types of star clusters can be distinguished: globular clusters are tight groups of hundreds to millions of old stars which are gravitationally bound, while open clusters, more loosely clustered groups of stars, generally contain fewer than a few hundred members, and are often very young. Open clusters become disrupted over time by the gravitational influence of giant molecular clouds as they move through the galaxy, but cluster members will continue to move in broadly the same direction through space even though they are no longer gravitationally bound; they are then known as a stellar association, sometimes also referred to as a moving group.
Galactic astronomy is the study of the Milky Way galaxy and all its contents. This is in contrast to extragalactic astronomy, which is the study of everything outside our galaxy, including all other galaxies.
The Magellanic Clouds are two irregular dwarf galaxies visible in the Southern Celestial Hemisphere; they are members of the Local Group and are orbiting the Milky Way galaxy. Because both show signs of a bar structure, they are often reclassified as Magellanic spiral galaxies. The two galaxies are:
Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, form part of the Hubble sequence. Most spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge. These are often surrounded by a much fainter halo of stars, many of which reside in globular clusters.
The Trifid Nebula is an H II region located in Sagittarius. It was discovered by Charles Messier on June 5, 1764. Its name means 'divided into three lobes'. The object is an unusual combination of an open cluster of stars; an emission nebula, a reflection nebula and a dark nebula. Viewed through a small telescope, the Trifid Nebula is a bright and peculiar object, and is thus a perennial favorite of amateur astronomers.
Gaia is a space observatory of the European Space Agency (ESA), launched in 2013 and expected to operate until c. 2022. The spacecraft is designed for astrometry: measuring the positions, distances and motions of stars with unprecedented precision. The mission aims to construct by far the largest and most precise 3D space catalog ever made, totalling approximately 1 billion astronomical objects, mainly stars, but also planets, comets, asteroids and quasars among others.
Sagittarius A* is a bright and very compact astronomical radio source at the center of the Milky Way, near the border of the constellations Sagittarius and Scorpius about 5.6° south of the ecliptic. It is the location of a supermassive black hole, similar to those generally accepted to be at the centers of most if not all spiral and elliptical galaxies.
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:
A dwarf galaxy is a small galaxy composed of about 100 million up to several billion stars, a small number compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is sometimes classified as a dwarf galaxy; others consider it a full-fledged galaxy. Dwarf galaxies' formation and activity are thought to be heavily influenced by interactions with larger galaxies. Astronomers identify numerous types of dwarf galaxies, based on their shape and composition.
The Milky Way is the galaxy that contains the 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. The term Milky Way is a translation of the Latin via lactea, from the Greek γαλαξίας κύκλος. From Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies.
A satellite galaxy is a smaller companion galaxy that travels on bound orbits within the gravitational potential of a more massive and luminous host galaxy. Satellite galaxies and their constituents are bound to their host galaxy, in the same way that planets within our own solar system are gravitationally bound to the Sun. While most satellite galaxies are dwarf galaxies, satellite galaxies of large galaxy clusters can be much more massive. The Milky Way is orbited by about fifty satellite galaxies, the largest of which is the Large Magellanic Cloud.
The Milky Way has several smaller galaxies gravitationally bound to it, as part of the Milky Way subgroup, which is part of the local galaxy cluster, the Local Group.
The Magellanic Stream, which contains a gaseous feature dubbed the leading arm, is a stream of high-velocity clouds of gas extending from the Large and Small Magellanic Clouds over 100° through the Galactic south pole of the Milky Way. The stream was sighted in 1965 and its relation to the Magellanic Clouds was established in 1974.
NGC 6357 is a diffuse nebula near NGC 6334 in the constellation Scorpius. The nebula contains many proto-stars shielded by dark disks of gas, and young stars wrapped in expanding "cocoons" or expanding gases surrounding these small stars. It is also known as the Lobster Nebula.
In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space.
An intergalactic star, also known as an intracluster star or a rogue star, is a star not gravitationally bound to any galaxy. Although a source of much discussion in the scientific community during the late 1990s, intergalactic stars are now generally thought to have originated in galaxies, like other stars, but later expelled as the result of either colliding galaxies or of a multiple star system travelling too close to a supermassive black hole, which are found at the center of many galaxies.
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 gas can be massive in size, some on the order of millions of times the mass of the Sun (), and cover large portions of the sky. They have been observed in the Milky Way's halo and within other nearby galaxies.
The Gaia Sausage is the remains of a dwarf galaxy, the Sausage Galaxy, or Gaia-Enceladus-Sausage, or Gaia-Enceladus, that merged with the Milky Way about 8–11 billion years ago. At least eight globular clusters were added to the Milky Way along with 50 billion solar masses of stars, gas and dark matter.
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