A blue dwarf is a predicted class of
star
A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
that develops from a
red dwarf
''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. ...
after it has exhausted much of its
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-to ...
fuel supply. Because red dwarfs
fuse
Fuse or FUSE may refer to:
Devices
* Fuse (electrical), a device used in electrical systems to protect against excessive current
** Fuse (automotive), a class of fuses for vehicles
* Fuse (hydraulic), a device used in hydraulic systems to protect ...
their hydrogen slowly and are fully
convective
Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the ...
(allowing their entire hydrogen supply to be fused, instead of merely that in the core), they are predicted to have lifespans of trillions of years; the
Universe
The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the univers ...
is currently not old enough for any blue dwarfs to have formed yet, but their future existence is predicted based on theoretical models.
[
]
Hypothetical scenario
Stars increase in 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 ...
as they age, and a more luminous star needs to radiate energy more quickly to maintain equilibrium. Stars larger than red dwarfs do this by increasing their size and becoming red giant
A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around o ...
s with larger surface areas. Rather than expanding, however, red dwarfs with less than 0.25 solar mass
The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...
es are predicted to increase their radiative rate by increasing their surface temperatures and becoming "bluer". This is because the surface layers of red dwarfs do not become significantly more opaque with increasing temperature.[
Despite their name, blue dwarfs do not necessarily increase in temperature enough to become blue stars. Simulations have been conducted on the future evolution of red dwarfs with stellar mass between 0.06 and 0.25 .][
Of the masses simulated, the bluest of the blue dwarf stars at the end of the simulation had begun as a 0.14 red dwarf, and ended with surface temperature approximately 8600 K, making it a type A blue-white star.
]
End of stellar life
Blue dwarfs eventually completely exhaust their store of hydrogen fuel, and their interior pressures are insufficient to fuse any other fuel. Once fusion ends, they are no longer main-sequence "dwarf" stars and become so-called white dwarf
A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes ...
s – which, despite the name, are ''not'' main-sequence "dwarfs" and are ''not'' stars, but rather stellar remnants.[
Once the former "blue"-dwarf stars have become degenerate, non-stellar ]white dwarf
A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes ...
s, they cool, losing the remnant heat left over from their final hydrogen-fusing stage. The cooling process also requires enormous periods of time – much longer than the age of the universe at present – similar to the immense time previously required for them to change from their original red dwarf
''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. ...
stage to their final blue dwarf stage. The stellar remnant white dwarf
A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes ...
will eventually cool to become a black dwarf. (The universe is not old enough for any stellar remnants to have cooled to "black", so black dwarfs are also a well-founded, but still hypothetical object.)
See also
* Lists of stars
*
References
{{Portal bar, Astronomy, Spaceflight, Outer space, Solar System
Hypothetical stars
Stellar evolution