NGC 4631 (also known as the Whale Galaxy or Caldwell 32) is a

barred spiral galaxy A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in about two thirds of all spiral galaxies, and generally affect both the motions of stars and interstellar gas within spiral galaxi ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Canes Venatici Canes Venatici () is one of the IAU designated constellations, 88 constellations designated by the International Astronomical Union (IAU). It is a small northern constellation that was created by Johannes Hevelius in the 17th century. Its name is ...

. This galaxy's slightly distorted wedge shape gives it the appearance of a herring or a whale, hence its nickname. Because this nearby galaxy is seen edge-on from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

, professional astronomers observe this galaxy to better understand the gas and stars located outside the plane of the galaxy.

Starburst and superwind

NGC 4631 contains a central starburst, which is a region of intense

star formation Star formation is the process by which dense regions within molecular clouds in The "medium" is present further soon.-->interstellar space

. The strong star formation is evident in the emission from

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

ized

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, an ...

and

interstellar dust Cosmic dust, also called extraterrestrial dust, star dust or space dust, is dust which exists in outer space, or has fallen on Earth. Most cosmic dust particles measure between a few molecules and 0.1 mm (100 micrometers). Larger particles are c ...

heated by the stars formed in the starburst. The most massive stars that form in star formation regions only burn hydrogen gas through

fusion Fusion, or synthesis, is the process of combining two or more distinct entities into a new whole. Fusion may also refer to: Science and technology Physics *Nuclear fusion, multiple atomic nuclei combining to form one or more different atomic nucl ...

for a short period of time, after which they explode as

supernovae A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when a ...

. So many supernovae have exploded in the center of NGC 4631 that they are blowing gas out of the plane of the galaxy. This

superwind A superwind is an extremely dense wind emanating from asymptotic giant branch stars towards the end of their lives. References Stellar evolution Stellar phenomena {{astronomy-stub ...

can be seen in

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

s and in

spectral line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...

emission. The gas from this superwind has produced a giant, diffuse corona of hot, X-ray emitting gas around the whole galaxy.

Nearby galaxies and galaxy group

NGC 4631 has a nearby companion

dwarf elliptical galaxy Dwarf elliptical galaxies, or dEs, are elliptical galaxies that are smaller than ordinary elliptical galaxies. They are quite common in galaxy groups and clusters, and are usually companions to other galaxies. Examples "Dwarf elliptical" galaxie ...

, NGC 4627. NGC 4627 and NGC 4631 together were listed in the ''

Atlas of Peculiar Galaxies The ''Atlas of Peculiar Galaxies'' is a catalog of peculiar galaxies produced by Halton Arp in 1966. A total of 338 galaxies are presented in the atlas, which was originally published in 1966 by the California Institute of Technology. The p ...

'' as an example of a "double galaxy" or a galaxy pair. NGC 4631 and NGC 4627 are part of the NGC 4631 Group, a group of galaxies that also includes the interacting galaxies NGC 4656 and NGC 4657. However, exact group identification is problematic because this galaxy and others lie in a part of the sky that is relatively crowded. Estimates of the number of galaxies in this group range from 5 to 27, and all studies identify very different member galaxies for this group.

References

External links

APOD (2004-01-23)
– The Whale Galaxy

– The Whale Galaxy (a better image) * *

– NGC 4631 {{DEFAULTSORT:NGC 4631 Barred spiral galaxies NGC 4631 Group Canes Venatici 4631 07865 42637 281 032b

Starburst and superwind

Nearby galaxies and galaxy group

See also

References

External links