Astrophysics (Index)About

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)
intensity mapping surveys
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

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