star formation
(SF)
(theorized collapse of gas and dust into stars)
Star formation (SF), the process by which stars are born,
is thought to be understood in outline,
but questions remain, perhaps more than for
models of subsequent stellar evolution.
Clouds sufficiently dense will undergo gravitational collapse
to achieve the density to trigger fusion, but among the remaining
questions is how and when this cloud density arises.
Molecular clouds (cold gas, gas that has cooled sufficiently
to form molecules) apparently sometimes develop patches dense enough
to collapse into stars, the areas of such activity known as stellar
nurseries or star-forming regions.
Some such dense regions may result from collisions of clouds, or
even whole galaxies.
Movement of cold gas, which would (sometimes) produce such high density can
be due to nearby supernovae and/or radiation pressure from nearby
early stars (radiation driven implosion or RDI).
For any of this to happen, there must exist available cold gas
within the galaxy and galaxy-accretion of cold gas from the
intergalactic medium increases the probability of star formation and can trigger
it as well.
As stars form, any nearby dust will be heated.
This spreads the heat energy, giving it a larger surface
and lower temperature, with a black-body spectrum concentrated
at longer wavelength electromagnetic radiation such as radio.
As a consequence, the presence of recent star formation can result
in short wavelengths from the early stars produced, but what is
sometimes observable is longer wavelengths from heated dust surrounding
the star formation.
As a general rule regarding galaxies, the more infrared it
emits (a sign of heated dust), the higher the star formation rate.
Star formation in distant galaxies
is of interest as the amount of star formation appears to have
grown and diminished over the history
of the universe (star formation history) and mechanisms that might do that are of interest.
H-alpha and the HI line are used to measure SF in distant
galaxies. Lyman alpha can also indicate distant SF and Lyman-alpha emitters are
presumed to have a very high SF rate.
The specifics of star formation of early stars are not as well understood
as for lower-mass stars because radiation pressure would
seem to limit the process. Theories include merging
lower-mass stars, or that the radiation is anisotropic, i.e.,
less in some direction(s), the lesser directions constituting a
"hole in the wall" through which gas accretion can continue.
As reflected in the initial mass function's greater-than-2 exponent, the vast majority of
star formation, by mass, is in later, lower mass stars, e.g., much
more mass amongst M-type stars than O-type stars. This means that one
useful sign of star formation in distant galaxies, the colors of
early stars, is imperfect because if some star formation
regions don't trigger whatever it is that creates high mass stars,
they could be missed.
The term quenching is used to indicate the cessation
of star formation, e.g., in a galaxy, which would be said
to become quiescent. For the long term,
a star-forming region is assumed to cease due to gas heating from
hot stars and supernovae (star formation feedback), followed by cooling and settling
and perhaps triggers from nearby events. Thus a long-term star formation rate
must be time-averaged over periods of high and low star formation.
Such an oscillation is termed episodic star formation.
Dwarf galaxies show evidence of this, e.g., through their
stellar demographics and the mechanism by which this happens is of
interest.
The term star and planet formation (SPF) covers star formation
and planet formation as well, which is believed to happen during
the first few million years of a star's life.
(stars)
Further reading:
https://en.wikipedia.org/wiki/Star_formation
https://pages.uoregon.edu/jimbrau/astr122/Notes/Chapter19.html
https://www.atnf.csiro.au/outreach/education/senior/astrophysics/stellarevolution_formation.html
https://pages.uoregon.edu/imamura/122/lecture-7/lecture-7.html
https://www.e-education.psu.edu/astro801/content/l5_p3.html
https://www.astro.umd.edu/~richard/ASTRO421/star%20formation.pdf
https://www.rpi.edu/dept/phys/Courses/ASTR2050/lec05Apr10am.pdf
Referenced by pages:
accretion
accretion rate
active galactic nucleus (AGN)
age-metallicity relation (AMR)
AIM-CO
alpha-enhanced
Balmer-break galaxy (BBG)
barrier
binding energy
bipolar outflow
blue horizontal branch (BHB)
Bok globule
brown dwarf (BD)
Butcher-Oemler effect (BOE)
Canadian Institute for Theoretical Astrophysics (CITA)
Carbon Monoxide Mapping Array (COMA)
CARMA EDGE
chemically peculiar star (CP star)
cloud
cloud fragmentation
cold gas
color-magnitude diagram (CMD)
computational astrophysics
CONCERTO
COPSS
core collapse supernova (CCSN)
cosmic gamma ray background (CGB)
cosmological distance
cosmological simulation
Cygnus-X
dark matter halo
DeGaS-MC
delay time distribution (DTD)
dendrogram
dense core
disk galaxy
Drake equation
dust echo
dusty galaxy
dwarf spheroidal galaxy (dSph)
EF Eridani
elliptical galaxy
emission line galaxy (ELG)
EMPIRE Survey
ESO 137-001
evaporating gas globule (EGG)
extinction
faint blue galaxy (FBG)
filament
FIRE Simulations
free-floating planet (FFP)
galactic wind
galaxy
Galaxy Evolution Explorer (GALEX)
galaxy formation
galaxy main sequence
galaxy merger
galaxy strangulation
gas flow
gas fraction
gas fraction estimation
giant molecular cloud (GMC)
giant planet formation
Gould's Belt
Hα survey
habitable zone (HZ)
Hall effect
Haro 29
HI gas mass
HII region (HII)
Hydrogen Accretion in Local Galaxies Survey (HALOGAS)
I Zwicky 18 (I Zw 18)
infrared excess (IRX)
inside-out growth
Institute of Theoretical Astrophysics (ITA)
intensity mapping (IM)
intergalactic HI cloud
interstellar medium (ISM)
ionized carbon fine structure line ([CII])
ionized hydrogen (HII)
Jeans length
jellyfish galaxy
Kelvin-Helmholtz instability (KHI)
Kennicutt-Schmidt law
KMOS3D
Large Millimeter Telescope (LMT)
lenticular galaxy (S0)
LINER
low mass star (LMS)
luminous infrared galaxy (LIRG)
Lyman alpha (Ly-α)
Lyman-alpha emitter (LAE)
Lyman-break galaxy (LBG)
Lyman-Werner photon
Lynds Catalog of Dark Nebulae (LDN)
Magellanic Clouds Photometric Survey (MCPS)
metallicity gradient
Milky Way (MW)
molecular cloud
molecular cloud turbulence
Molecular Deep Field
Orion Molecular Cloud Complex
pea galaxy (GP)
peak star-formation epoch
PEP
PHIBSS
Population III (Pop III)
post-starburst galaxy (PSB galaxy)
protogalaxy
pseudobulge
quenched galaxy
radial mixing
radio galaxy (RG)
REBELS
red and dead
ring galaxy
RT instability
SAGE
SBS 0335-052
Serpens Cloud
Sgr B2
shell
shell galaxy
shock wave
SIMBA
Sloan Digital Sky Survey (SDSS)
SMBH formation
Smith Cloud
sound speed
spectral energy distribution (SED)
spectroscopic parallax
Spindle Galaxy (NGC 5866)
spiral arm
spiral galaxy
star
star formation feedback
star formation history (SFH)
star formation rate (SFR)
star-formation rate stellar-mass ratio
star-forming region (SFR)
starburst galaxy
STARBURST99
STARFORGE
stellar association
stellar astronomy
stellar demographics
stellar evolution
stellar halo
stellar kinematics
submillimeter astronomy
submillimeter galaxy (SMG)
supershell
The Survey for Ionization in Neutral Gas Galaxies (SINGG)
thermal dust emission
thick disk
thin disk
tidal arm
Tomographic Ionized-carbon Mapping Experiment (TIME)
Toomre Q parameter (Q)
ultra diffuse galaxy (UDG)
ultraluminous infrared galaxy (ULIRG)
UVJ diagram
wide binaries (WB)
[α/Fe] versus [Fe/H] diagram
Index