An Etymological Dictionary of Astronomy and Astrophysics

A → Seyfert galaxy, which is the central, dominant member of the large and relatively nearby → Perseus cluster of galaxies.
A powerful source of X-rays and radio emission, NGC 1275 accretes matter (→ accretion) as
intercluster material falls into it, ultimately feeding a → supermassive black hole (SMBH) at the galaxy’s core. NGC 1275, hosts a narrow-line radio source, Perseus A (3C 84), which interacts with the intracluster gas through its jets and bipolar outflows.

See also: NGC, → New General Catalogue.

A → Seyfert galaxy, which is the central, dominant member of the large and relatively nearby → Perseus cluster of galaxies.
A powerful source of X-rays and radio emission, NGC 1275 accretes matter (→ accretion) as
intercluster material falls into it, ultimately feeding a → supermassive black hole (SMBH) at the galaxy’s core. NGC 1275, hosts a narrow-line radio source, Perseus A (3C 84), which interacts with the intracluster gas through its jets and bipolar outflows.

See also: NGC, → New General Catalogue.

A prominent → star cluster, and the ionizing core of giant → H II region → N66 in the → Small Magellanic Cloud galaxy. NGC 346 hosts the largest sample of young, → massive stars in the whole SMC, containing 33 → O-type stars among which 11 are of type O6.5 or earlier. This is young massive star cluster with an estimated age of about 3 million years.

See also: 346, a serial number in the → New General Catalogue.

A prominent → star cluster, and the ionizing core of giant → H II region → N66 in the → Small Magellanic Cloud galaxy. NGC 346 hosts the largest sample of young, → massive stars in the whole SMC, containing 33 → O-type stars among which 11 are of type O6.5 or earlier. This is young massive star cluster with an estimated age of about 3 million years.

See also: 346, a serial number in the → New General Catalogue.

The most massive and luminous visible → starburst region in the Galaxy. This is our local → giant H II region lying at a distance of about 6-7 kpc in the → Carina arm (→ right ascension = 11h, → declination = -61°). Its central starburst cluster hosts the largest known concentration of extremely young, mostly unevolved → high-mass stars in the Galaxy. With an age of only 1-2 Myr for its most massive stars, NGC 3603 is one of the youngest starburst clusters known.
It has about 40 known → O stars and → W-R stars, producing a → Lyman continuum flux of 10⁵¹ s^-1, about 100 times the ionizing
power of the Orion → Trapezium cluster.
The OB stars contribute to more than 2000 → solar masses to the cluster mass. With a bolometric luminosity over 10⁷→ solar luminosities, NGC 3603 has about 10% of the luminosity of → 30 Doradus and looks in many respects very similar to its core, → R136. A total mass of 7,000 solar masses is measured in the inner 1 pc from the cluster center, whereas the → low-mass stars extend out to at least 5 pc. The mass segregated core of the
cluster, with 10⁵ solar masses per pc³, displays the highest local stellar density outside the Galactic Center region. The spectral
analysis of the W-R like massive component in the cluster core (→ HD 97950) suggests a → metallicity close or equal to solar (See, e.g., Melena et al. 2008, AJ 135, 878, and references therein).

See also: 3603, a serial number in the → New General Catalogue.

The most massive and luminous visible → starburst region in the Galaxy. This is our local → giant H II region lying at a distance of about 6-7 kpc in the → Carina arm (→ right ascension = 11h, → declination = -61°). Its central starburst cluster hosts the largest known concentration of extremely young, mostly unevolved → high-mass stars in the Galaxy. With an age of only 1-2 Myr for its most massive stars, NGC 3603 is one of the youngest starburst clusters known.
It has about 40 known → O stars and → W-R stars, producing a → Lyman continuum flux of 10⁵¹ s^-1, about 100 times the ionizing
power of the Orion → Trapezium cluster.
The OB stars contribute to more than 2000 → solar masses to the cluster mass. With a bolometric luminosity over 10⁷→ solar luminosities, NGC 3603 has about 10% of the luminosity of → 30 Doradus and looks in many respects very similar to its core, → R136. A total mass of 7,000 solar masses is measured in the inner 1 pc from the cluster center, whereas the → low-mass stars extend out to at least 5 pc. The mass segregated core of the
cluster, with 10⁵ solar masses per pc³, displays the highest local stellar density outside the Galactic Center region. The spectral
analysis of the W-R like massive component in the cluster core (→ HD 97950) suggests a → metallicity close or equal to solar (See, e.g., Melena et al. 2008, AJ 135, 878, and references therein).

See also: 3603, a serial number in the → New General Catalogue.

A → binary star lying in the core of the Galactic → giant H II region  → NGC 3603. NGC 3603-A1 is double-eclipsing → Wolf-Rayet binary of type → WN6ha with an orbital period of 3.77 days. Their masses have been derived to be

M1 = (116 ± 31) Msun for the primary and M2 = (89 ± 16) Msun for the secondary component of A1. The primary in A1 is the most massive star weighed so far (Schnurr et al., 2008, MNRAS 389, L38).

See also: → NGC 3603.

A → binary star lying in the core of the Galactic → giant H II region  → NGC 3603. NGC 3603-A1 is double-eclipsing → Wolf-Rayet binary of type → WN6ha with an orbital period of 3.77 days. Their masses have been derived to be

M1 = (116 ± 31) Msun for the primary and M2 = (89 ± 16) Msun for the secondary component of A1. The primary in A1 is the most massive star weighed so far (Schnurr et al., 2008, MNRAS 389, L38).

See also: → NGC 3603.

A galaxy discovered in 1784 by William Herschel that happens to lie nearly along the line of sight to the star → Beta Andromedae. More specifically, it lies at an angular separation of seven arc-minutes. For this reason it is known also as → Mirach’s Ghost. NGC 404 is in fact a → dwarf galaxy lying at a distance of about 10 million → light-years (3.07 ± 0.37 Mpc). NGC 404 harbors a low-luminosity → active galactic nucleus powered by the lowest-mass (< 150,000 Msun) central → massive black hole (Nyland et al., 2017, ApJ 845, 50).

See also: NGC, → New General Catalogue.

A galaxy discovered in 1784 by William Herschel that happens to lie nearly along the line of sight to the star → Beta Andromedae. More specifically, it lies at an angular separation of seven arc-minutes. For this reason it is known also as → Mirach’s Ghost. NGC 404 is in fact a → dwarf galaxy lying at a distance of about 10 million → light-years (3.07 ± 0.37 Mpc). NGC 404 harbors a low-luminosity → active galactic nucleus powered by the lowest-mass (< 150,000 Msun) central → massive black hole (Nyland et al., 2017, ApJ 845, 50).

See also: NGC, → New General Catalogue.

A → lenticular galaxy (S0) in → Hydra constellation located about 130 million → light-years (40 ± 8 Mpc, → redshift z = 0.009680) from Earth, discovered by William Herschel in 1789. On 17 August 2017 the → Laser Interferometer Gravitational-Wave Observatory (LIGO) and the → Virgo Interferometer both detected → gravitational waves (→ GW170817) from the collision of two → neutron stars within this galaxy. The → electromagnetic counterpart GRB 170817A was detected 1.7 seconds later. The event was associated with a → kilonova offset 10.6 arcsec (corresponding to 2.0 kpc) to north-east from the nucleus of NGC 4993.

See also: NGC, → New General Catalog

A → lenticular galaxy (S0) in → Hydra constellation located about 130 million → light-years (40 ± 8 Mpc, → redshift z = 0.009680) from Earth, discovered by William Herschel in 1789. On 17 August 2017 the → Laser Interferometer Gravitational-Wave Observatory (LIGO) and the → Virgo Interferometer both detected → gravitational waves (→ GW170817) from the collision of two → neutron stars within this galaxy. The → electromagnetic counterpart GRB 170817A was detected 1.7 seconds later. The event was associated with a → kilonova offset 10.6 arcsec (corresponding to 2.0 kpc) to north-east from the nucleus of NGC 4993.

See also: NGC, → New General Catalog

A → lenticular galaxy in the constellation of the → Draco. It lies about 50 million → light-years (15.3 Mpc) distant and has a size of about 60,000 light-years. Due to its thin → rdge-on appearance, it is also called the → Spindle Galaxy. Known also as Messier 102.

See also: 5866, a serial number in the → New General Catalogue.

A → lenticular galaxy in the constellation of the → Draco. It lies about 50 million → light-years (15.3 Mpc) distant and has a size of about 60,000 light-years. Due to its thin → rdge-on appearance, it is also called the → Spindle Galaxy. Known also as Messier 102.

See also: 5866, a serial number in the → New General Catalogue.

A → reflection nebula located in the constellation → Cepheus at a distance of 1,300 → light-years. It was discovered by Sir William Herschel on October 18, 1794. The nebula, also known as the → Iris Nebula and → Caldwell 4, is about 6 light-years across.

At the center of NGC 7023 lies an extremely young star named V380 Cep or SAO 19158 (mag. +7.1), which is associated with plenty of local dust.

NGC 7023 is located 6 degrees northwest of the brightest star in Cepheus, Alderamin (α Cep - mag. +2.5) with third magnitude Alfirk (Beta Cephei) positioned about 3.5 degrees to the northeast. Only a degree east-northeast of NGC 7023 is Mira type variable star T Cep, which fluctuates between magnitudes +5.2 and +11.3 over a period of 388.14 days.

See also: 7023, a serial number in the → New General Catalogue.

A → reflection nebula located in the constellation → Cepheus at a distance of 1,300 → light-years. It was discovered by Sir William Herschel on October 18, 1794. The nebula, also known as the → Iris Nebula and → Caldwell 4, is about 6 light-years across.

At the center of NGC 7023 lies an extremely young star named V380 Cep or SAO 19158 (mag. +7.1), which is associated with plenty of local dust.

NGC 7023 is located 6 degrees northwest of the brightest star in Cepheus, Alderamin (α Cep - mag. +2.5) with third magnitude Alfirk (Beta Cephei) positioned about 3.5 degrees to the northeast. Only a degree east-northeast of NGC 7023 is Mira type variable star T Cep, which fluctuates between magnitudes +5.2 and +11.3 over a period of 388.14 days.

See also: 7023, a serial number in the → New General Catalogue.