![Superbubble N70 in LMC](https://upload.wikimedia.org/wikipedia/commons/6/67/Superbubble_N70_in_LMC.jpg)
A superbubble or supershell is a cavity which is hundreds of light years across and is populated with hot (10
6 K) gas atoms, less dense than the surrounding
interstellar medium
In astronomy, the interstellar medium is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstella ...
, blown against that medium and carved out by multiple
supernova
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 ...
e and
stellar wind
A stellar wind is a flow of gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric.
D ...
s. The winds, passage and gravity of newly born stars strip superbubbles of any other dust or gas. The
Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
lies near the center of an old superbubble, known as the
Local Bubble
The Local Bubble, or Local Cavity, is a relative cavity in the interstellar medium (ISM) of the Orion Arm in the Milky Way. It contains the closest of celestial neighbours and among others, the Local Interstellar Cloud (which contains the Sol ...
, whose boundaries can be traced by a sudden rise in
dust
Dust is made of fine particles of solid matter. On Earth, it generally consists of particles in the atmosphere that come from various sources such as soil lifted by wind (an aeolian process), volcanic eruptions, and pollution. Dust in homes ...
extinction
Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
of exterior stars at distances greater than a few hundred light years.
Formation
The most massive stars, with masses ranging from eight to roughly one hundred solar masses and
spectral type
In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...
s of O and early B, are usually found in groups called OB associations. Massive O stars have strong stellar winds, and most of these stars explode as
supernova
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 ...
e at the end of their lives.
The strongest stellar winds release kinetic energy of 10
51 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 (10
44 J) over the lifetime of a star, which is equivalent to a supernova explosion. These winds can form
stellar wind bubbles dozens of light years across.
Inside
OB associations, the stars are close enough that their wind bubbles merge, forming a giant bubble called a superbubble.
When stars die, supernova explosions, similarly, drive
blast wave
In fluid dynamics, a blast wave is the increased pressure and flow resulting from the deposition of a large amount of energy in a small, very localised volume. The flow field can be approximated as a lead shock wave, followed by a self-similar sub ...
s that can reach even larger sizes, with expansion velocities up to several hundred km s
−1. Stars in OB associations are not gravitationally bound, but they drift apart at small speeds (of around 20 km s
−1), and they exhaust their fuel rapidly (after a few millions of years). As a result, most of their supernova explosions occur within the cavity formed by the stellar wind bubbles. These explosions never form a visible
supernova remnant
A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar mat ...
, but instead expend their energy in the hot interior as sound waves. Both stellar winds and stellar explosions thus power the expansion of the superbubble in the interstellar medium.
The interstellar gas swept up by superbubbles generally cools, forming a dense shell around the cavity. These shells were first observed in line emission at
twenty-one centimeters from
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 ...
, leading to the formulation of the theory of superbubble formation. They are also observed 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 ...
emission from their hot interiors, in optical line emission from their ionized shells, and in infrared continuum emission from dust swept up in their shells. X-ray and visible emission are typically observed from younger superbubbles, while older, larger objects seen in twenty-one centimeters may even result from multiple superbubbles combining, and so are sometimes distinguished by calling them ''supershells''.
Large enough superbubbles can blow through the entire galactic disk, releasing their energy into the surrounding galactic halo or even into the
intergalactic medium
Intergalactic may refer to:
* "Intergalactic" (song), a song by the Beastie Boys
* ''Intergalactic'' (TV series), a 2021 UK science fiction TV series
* Intergalactic space
* Intergalactic travel, travel between galaxies in science fiction and sp ...
.
Examples
*
LHA 120-N 44 (N44) in the Large Magellanic Cloud.
*
Anticenter shell
The anticenter shell or anticenter superbubble is a region near the anticenter of the Milky Way Galaxy that emits 21 cm radiation. It is located at , or l = 197°, b = +2° in galactic coordinates, near the border of the constellations Gemini a ...
, a supershell once called "Snickers"
* Henize 70
[ Henize 70: A SuperBubble In The LMC]
Astronomy Picture of the Day
Astronomy Picture of the Day (APOD) is a website provided by NASA and Michigan Technological University (MTU). According to the website, "Each day a different image or photograph of our universe is featured, along with a brief explanation written ...
, 1999-11-30
* Monogem Ring
*
Ophiuchus Superbubble
The Ophiuchus Superbubble is an astronomical phenomenon located in the Ophiuchus constellation, with a center around ℓ ≈ 30 °. This giant superbubble was first discovered in a 2007 study of extraplanar neutral hydrogen in the disk-halo trans ...
* The Scutum Supershell
*
Orion-Eridanus Superbubble
* The Perseus-Taurus Shell
* The
Local Bubble
The Local Bubble, or Local Cavity, is a relative cavity in the interstellar medium (ISM) of the Orion Arm in the Milky Way. It contains the closest of celestial neighbours and among others, the Local Interstellar Cloud (which contains the Sol ...
Image gallery
References
External links
* Tenorio-Tagle, G., & Bodenheimer, P.
Large-scale expanding superstructures in galaxies. 1988, ''
Annual Review of Astronomy and Astrophysics'' 26, 145–197. General overview.
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Galactic astronomy
Interstellar media
Supernovae