Astrophysics (Index)About

mass

(object's quality that determines the effects of forces and gravity)

Mass is the quality of an object that determines its gravity and also determines the degree of acceleration resulting from a force on the object. The term is also used for a measure of this quality associated with such an object. It is the quality that determines an object's weight when it is within a gravitational field, e.g., on the Earth's surface.

Mass was once considered an absolutely conserved value, but famously, the equation e=mc² adjusted that idea: mass is conserved in many "everyday" cases, but is considered a form or aspect of energy, the latter of which is conserved universally.

The above gravitational and acceleration/inertia effects are found to be proportional, suggesting they both result from the same quality. This is, in fact, tested with experiments measuring the degree to which this proportion holds, and no credible discrepancy has been found. (These two apparently-equivalent qualities are termed the inertial mass and the gravitational mass.)

Relativity has consequences regarding the meaning of the term mass. For an object at rest, the concept is straight-forward, but from a frame of reference in which the object is moving, acceleration also depends upon the speed at which it is moving, as if the moving object's mass were greater. The term rest mass is clear, and currently, it is common to treat the term mass as rest mass, and call the apparent quality of such a moving object a relativistic mass (or else avoid referring to it). At one time, this consensus wasn't as clear and some earlier writing may treat the term mass as this relativistic mass, and the point of this is you must sometimes assure you know which meaning is intended.

Mass (taken as rest mass) makes the equation e=mc² true when the object is at rest, and otherwise does not include the effects of its motion (relativistic kinetic energy). If m were to be taken as the relativistic mass, then the equation would include both its rest energy and the effects of its motion. One means of describing the impossibility of accelerating an object to the speed of light is that its relativistic mass would be pushed toward infinity as you near that speed.

The term dynamic mass refers to the mass of a body determined through dynamics, e.g., using orbital periods. This requires knowledge (at minimum) of either the distance from Earth or the mass of another object within the gravitationally-bound system.

The term point mass refers to a modeling an object's mass as being at a single point. This simplifies problems and can be a very useful approximation if distances between objects are large compared to their size and/or if an object is close to being spherically symmetric.

Among the units of mass used in astrophysics:

electron volt very small sub-atomic particles 1.78×10-36 kg using e=mc²
dalton atoms/molecules 1.66053892×10-27 kg roughly the mass of a hydrogen atom
Planck mass a "natural" unit 2.18×10-8 kg
kilogram (& gram) general SI units
Moon mass moons and small planets 7.3×1022 kg 0.012 Earth mass (1.2%)
Earth mass planets 5.972×1024 kg
Jupiter mass large planets 1.898×1027 kg 318 Earth masses or 0.001 solar mass (0.1%)
solar mass stars and larger objects 2×1030 kg 333,000 Earth masses

A mass number is a count of nucleons in a nucleus, atom or molecule. Nucleons (i.e., protons and neutrons) have roughly the same mass and the mass number is an approximation of the mass of the particle in daltons.


The term mass can be used to mean (roughly) substance, i.e., something that has mass, in phrases like mass transfer, mass loading, and coronal mass ejection.


(physics,relativity,measure)
Further reading:
https://en.wikipedia.org/wiki/Mass
https://en.wikipedia.org/wiki/Mass_in_special_relativity
http://hyperphysics.phy-astr.gsu.edu/hbase/mass.html
https://astronomy.swin.edu.au/cosmos/m/Mass
https://www.britannica.com/science/mass-physics
https://www.qrg.northwestern.edu/projects/vss/docs/propulsion/2-why-is-mass-important.html

Referenced by pages:
1.3-mm observation
21-cm line
2M1207
3C 348
51 Eridani b
51 Pegasi b (51 Peg b)
55 Cancri e (55 Cnc e)
A-type star (A)
AB Aurigae (AB Aur)
AB Pictoris (AB Pic)
Abell 1689 (A1689)
Abell 85 (A85)
absorption coefficient
accretion
accretion rate
Achernar
active galactic nucleus (AGN)
active galaxy
AD Leonis (AD Leo)
admittance
Algol (Beta Per)
Alpha Centauri (α Centauri)
alpha CO (αCO)
aluminum (Al)
anomalous X-ray pulsar (AXP)
anti-de Sitter space (AdS)
Arcturus
asteroseismology
astronomical quantities
asymptotic giant branch (AGB)
atmosphere
atmospheric escape
atomic dark matter (aDM)
AU Microscopii (AU Mic)
autoconversion rate
Avogadro's number (NA)
axion (A0)
Axion Dark Matter Experiment (ADMX)
B-type star (B)
Barnard's Star
barrier
barycenter
baryon
baryonic matter
beta decay
Beta Pictoris b (β Pic b)
Betelgeuse
bigravity
binary black hole (BBH)
binary SMBH (BSMBH)
binary star
Birkhoff's theorem
black hole (BH)
black hole binary (BHB)
black hole mass function (BHMF)
black hole merger
black hole model
Black Widow Pulsar (B1957+20)
black-hole information paradox
Bouguer anomaly
brown dwarf (BD)
bulk density
Bullet Cluster
Callisto
Canadian Cluster Comparison Project (CCCP)
Canopus
Capella
carbon (C)
carbon burning
carbon monoxide (CO)
Cassini
Ceres
Chandrasekhar limit
CHEOPS
CHIPS
chirp mass (Mc)
cluster radius
CNO cycle
CO to H2 factor (XCO)
COCONUTS
cold dark matter (CDM)
COLD GASS
color-magnitude diagram (CMD)
column density
common envelope (CE)
comoving units
Compton wavelength
conditional luminosity function (CLF)
conditional stellar mass function (CSMF)
conservation law
continuous gravitational wave
convection zone
core accretion model
core collapse
core collapse supernova (CCSN)
coronal mass ejection (CME)
Cosmic Lens All-sky Survey (CLASS)
cosmic neutrino background (CNB)
cosmic variance
cosmological simulation
cosmological zoom simulation
critical density (ρc)
Cryogenic Dark Matter Search (CDMS)
cyclotron radiation emission spectroscopy (CRES)
dalton (Da)
damped Lyman alpha absorber (DLA)
dark energy (Λ)
dark matter (DM)
dark matter annihilation
dark matter detector
dark matter halo
Dartmouth Stellar Evolution Database (DSED)
Deep Lens Survey (DLS)
dense core
dense core mass function (DCMF)
density parameter
deuterium (D)
deuterium burning
dex
direct collapse black hole (DCBH)
DM Tau
double-line spectroscopic binary (SB2)
dredge-up
drogue chute
dwarf galaxy problem
Earth
Earth analog
eclipsing binary (E)
Eddington luminosity
EF Eridani
Einstein delay
ejection
electric field (E)
electron (e-)
electron capture
electron capture supernova
electron degenerate matter (EDM)
electron shell
electron volt (eV)
element
endothermic reaction
energy
Epsilon Eridani (ε Eridani)
Epsilon Indi (ε Indi)
escape velocity (Ve)
Europa
Europa Clipper
event horizon (EH)
evolutionary track
exo-Earth
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extreme mass ratio inspiral (EMRI)
F-type star (F)
failed binary
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Friedmann model
fusion
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G-type star (G)
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GG Tau
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GJ 1132 b
GJ 1214 b
Gliese 436 b (GJ 436 b)
gravimetry
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gravitational field
gravitational instability model
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gravitational potential energy
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HD 163296
HD 189733 b
HD 209458 b
HD 80606 b
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Henyey track
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HI gas mass
high-velocity cloud (HVC)
Hill radius
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HR 8799
Hubble expansion
Hulse-Taylor Binary (PSR B1913+16)
humidity
hydrodynamic equations
hydrogen (H)
hydrology
hydrostatic equilibrium
hypermassive neutron star (HMNS)
inflated radii
initial mass function (IMF)
innermost stable circular orbit (ISCO)
intermediate-mass black hole (IMBH)
intracluster medium (ICM)
Io
IRAS 13224-3809
iron (Fe)
isochronal fitting
isolation mass
J1407
J2
Jacobi integral
Jeans equations
Jeans length
Jeans parameter (λ)
Jupiter
K-type star (K)
K2-18b
Kapteyn's Star
KATRIN
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Kepler-1625b
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Kepler-79
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kilometer size barrier
kinetic energy (KE)
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Lacaille 9352
Lagrangian point
Lalande 21185
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Laplace radius (rL)
LARES
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large scale structure (LSS)
LB-1
Lee-Weinberg bound
Legendre polynomials
LHS 1140
LHS 3844 b
libration
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long gamma-ray burst (LGRB)
Love number
low mass star (LMS)
low-surface-brightness galaxy (LSB galaxy)
luminous blue variable (LBV)
LUX
Luyten 726-8
M-sigma relation
M-type star (M)
M87*
Mach's principle
MACHO
magnesium (Mg)
main sequence star (MS)
main-sequence lifetime (MS lifetime)
Mars
maser
mass density
mass fraction
mass function
mass loading
mass loss
mass number (A)
mass ratio (μ)
mass shell
mass spectrometer
mass-luminosity relation
mass-radius relation
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Maxwell-Boltzmann distribution
mean molecular weight (μ)
mega-Earth
Mercury
metallicity (Z)
meteoroid
methane (CH4)
metric
Milkomeda
Milky Way (MW)
mini-Neptune
minimum mass (m sin i)
mirror support cell
mixing ratio
modified Newtonian dynamics (MOND)
moment of inertia factor
moon
MUSCLES
MWC 758
Navarro-Frenk-White profile (NFW profile)
NEO Surveyor
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neutron star (NS)
neutron star merger
Newton's laws
NGC 3201
Nice model
no-hair theorem
nuclear energy generation rate (ε)
nuclear statistical equilibrium (NSE)
nutation
O-type star (O)
O5 spectral type (O5)
OGLE-2005-BLG-390Lb
oligarch
open cluster (OC)
oxygen (O)
oxygen burning
P-Pdot diagram
pair production
pair-instability supernova (PISN)
parameterized post-Newtonian formalism (PPN formalism)
particle spectrometer
Perseus Cluster (Abell 426)
photodisintegration
photon
PIC simulation
Planck units
planet
planet demographics
planet formation
Planet Nine
planetary mass object (PMO)
planetary migration
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planetesimal
plasma frequency
plasma wave
Pluto
plutoid
Poisson's equation
Population III (Pop III)
positron (e+)
post-common-envelope binary (PCEB)
post-main-sequence star
Poynting-Robertson effect
pre-main-sequence star (PMS)
Press-Schechter formalism
pressure integral
primary
primordial black hole (PBH)
probability mass function (PMF)
Procyon
Project 8
projected semi-major axis
protostar
Proxima b
Psyche
pulsar (PSR)
Q factor
quark
quasi-periodic oscillation (QPO)
radial velocity method
radiation pressure
rare designator prefixes
red clump (RC)
red dwarf
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red-giant branch (RGB)
reduced mass
relativistic energy
relativistic invariance
relativistic momentum
repulsive dark matter (RDM)
retrograde accretion
reverberation mapping
RHAPSODY
Rigel
Roche limit
Rosetta
Ross 154
Ross 248
rotation curve
RR Lyrae variable (RRL)
S-Star Cluster
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Sag A*
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Saturn
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Schwarzschild radius (RS)
self-gravitation
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silicon burning
Sirius
SMBH formation
solar mass (MSun)
solar nebula
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specific angular momentum (J)
specific heat
specific volume
spectral class
spectrometer
spectrometry
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spicule
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Spitzer Extended Deep Survey (SEDS)
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standard gravitational parameter (μ)
star
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star-formation rate stellar-mass ratio
stellar birth rate function
stellar core
stellar demographics
stellar distance determination
stellar evolution
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stellar mass determination
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stellar radius determination
stellar structure
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Sun
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synchronous orbit
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T Tauri
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Thomson scattering
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time-delay cosmology
timescale (t)
Titan
TOI 700 d
Tolman-Oppenheimer-Volkoff limit (TOV)
traditional approximation of rotation (TAR)
transit timing variations (TTV)
TRAPPIST-1
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Triton
Tully-Fisher relation (TFR)
turn-off point (TO)
TW Hydrae (TW Hya)
Type Ia supernova problem
Uranus
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variable star
Vega
velocity dispersion (σ)
Venus
virial parameter
virial theorem
VLT-FLAMES Tarantula Survey (VFTS)
Vogt-Russell theorem (VR theorem)
VY Canis Majoris (VY CMa)
WASP-12b
WASP-33b
WASP-43b
WASP-67b
water world
water-ice planet
weak lensing (WL)
white dwarf (WD)
WIMP
WISE 0855-0714 (W0855)
WISE 1534-1043
Wolf 359
Wolf-Rayet galaxy
wormhole
WR 104
WR 140
X-ray binary (XRB)
X-ray burster (XRB)
XO-3b
Y-type star (Y)

Index