NGC 7424 is a barred spiral galaxy located 37.5 million light-years away in the

southern Southern may refer to: Businesses * China Southern Airlines, airline based in Guangzhou, China * Southern Airways, defunct US airline * Southern Air, air cargo transportation company based in Norwalk, Connecticut, US * Southern Airways Express, M ...

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 ...

Grus (the Crane). Its size (about 100,000

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s) makes it similar to our own

galaxy A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. ...

, the

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 ...

. It is called a " grand design" galaxy because of its well defined spiral arms. One supernova and two ultraluminous X-ray sources have been discovered in NGC 7424.

Characteristics

NGC 7424 is intermediate between normal spirals (SA) and strongly barred galaxies (SB). Other features include the presence of a central ring-like structure and a relatively low core brightness relative to the arms. The redder color of the prominent bar indicates an older population of stars while the bright blue color of the loose arms indicates the presence of ionised hydrogen and clusters of massive young stars. NGC 7424 is listed as a member of the IC 1459 Grus Group of galaxies, but is suspected of being a "

field galaxy A field galaxy is a galaxy that does not belong to a larger galaxy group or cluster and hence is gravitationally alone. Roughly 80% of all galaxies located within of the Milky Way are in groups or clusters of galaxies. Most low-surface-brightne ...

"; that is, not gravitationally bound to any group.

Supernova 2001ig

SN 2001ig was a rare

Type IIb supernova A Type II supernova (plural: ''supernovae'' or ''supernovas'') results from the rapid collapse and violent explosion of a massive star. A star must have at least 8 times, but no more than 40 to 50 times, the mass of the Sun () to undergo this ...

discovered by Australian amateur Robert Evans on the outer edge of NGC 7424 on 10 December 2001. Type IIb supernovae (SNe) initially exhibit

spectral lines 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 ident ...

of hydrogen (like typical Type II's), but these disappear after a short time to be replaced by lines of oxygen, calcium and magnesium (like typical Type Ib's and Ic's). HST image of surviving companion to supernova SN 2001ig

HST image of surviving companion to supernova SN 2001ig

In 2006,

Anglo-Australian Observatory The Australian Astronomical Observatory (AAO), formerly the Anglo-Australian Observatory, was an optical and near-infrared astronomy observatory with its headquarters in North Ryde in suburban Sydney, Australia. Originally funded jointly by the U ...

astronomer Stuart Ryder et al. found what they argued could be the binary companion to SN 2001ig using the Gemini Observatory. It is a massive A or F class star that had an

eccentric orbit In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values betw ...

around the progenitor, a Wolf-Rayet star. They believe that the companion periodically stripped the outer hydrogen-rich envelope of the progenitor, accounting for the observed spectral changes. Princeton University fellow

Alicia Soderberg Alicia Margarita Soderberg (born 1977) is an American astrophysicist whose research focused on supernovae. She was an assistant professor of astronomy at Harvard University and a postdoctoral fellow at the Harvard-Smithsonian Center for Astrophy ...

et al. also believe that the progenitor was a Wolf-Rayet star, but suggest that the periodic mass loss was a result of the intense stellar wind these stars produce. In a paper published in March 2018, Ryder et al. announced that the surviving companion had been observed with the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...

in the ultraviolet. This is the first time a companion to a Type IIb supernova has been imaged.

Ultraluminous X-ray sources

In May and June 2002, Roberto Soria and his colleagues at the Harvard-Smithsonian Center for Astrophysics discovered two

Ultraluminous X-ray source An ultraluminous X-ray source (ULX) is an astronomical source of X-rays that is less luminous than an active galactic nucleus but is more consistently luminous than any known stellar process (over 1039 erg/s, or 1032 watts), assuming that it radiat ...

s (ULXs) with the

Chandra X-ray Observatory The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space telescope launched aboard the during STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources 1 ...

. ULXs are objects that emit tremendous amounts of

X-rays 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 Picometre, picometers to 10 Nanometre, nanometers, corresponding to frequency, ...

(> 10³²

watt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wa ...

s or 10³⁹

erg The erg is a unit of energy equal to 10−7joules (100 nJ). It originated in the Centimetre–gram–second system of units (CGS). It has the symbol ''erg''. The erg is not an SI unit. Its name is derived from (), a Greek word meaning 'work' o ...

/ s), assuming they radiate

isotropic Isotropy is uniformity in all orientations; it is derived . Precise definitions depend on the subject area. Exceptions, or inequalities, are frequently indicated by the prefix ' or ', hence ''anisotropy''. ''Anisotropy'' is also used to describe ...

ally (the same in all directions). This amount is larger than currently understood stellar processes (including supernovae) but smaller than the amount of

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 emitted by active galactic nuclei, which accounts for their alternate name, Intermediate-luminosity X-ray Objects (IXOs). The source designated ULX1 was found in a relatively empty interarm region, far from any bright clusters or star-forming complexes, and showed a 75% increase in X-ray

luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...

over the course of 20 days. ULX2 was found in an exceptionally bright young stellar complex, and showed an order of magnitude increase over the same time period.

References

External links

* {{DEFAULTSORT:NGC 7424 Barred spiral galaxies Grus (constellation) 7424 070096