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high-velocity star

A star moving faster than 65 km/s relative to the average motion of the stars in the Sun's neighbourhood (the local standard of rest). High-velocity stars are members of the galactic halo, ...

high-velocity star

high-velocity star   Quick reference

A Dictionary of Astronomy (3 ed.)

Reference type:
Subject Reference
Current Version:
2018

...-velocity star A star moving faster than 65 km/s relative to the average motion of the stars in the Sun’s neighbourhood (the local standard of rest ). High-velocity stars are members of the galactic halo, moving in highly elliptical orbits around the galactic centre. Their high relative velocities result from the fact that they are passing through the galactic disk and do not share the rotation of the Sun and its neighbouring stars around the galactic centre. Such stars may have formed early in the Galaxy’s history, or they may be remnants of smaller...

high-velocity star

high-velocity star  

A star moving faster than 65 km/s relative to the average motion of the stars in the Sun's neighbourhood (the local standard of rest). High-velocity stars are members of the galactic halo, moving in ...
runaway star

runaway star  

A young star moving at high velocity, perhaps hundreds of kilometres per second, suggesting that it has been ejected by some violent event from its birthplace. Such stars were probably once part of a ...
halo population

halo population  

Those stars which belong to the spherical halo surrounding our Galaxy and others. Such stars have a low content of heavy elements, belong to Population II, and are believed to be older than most ...
Herbig–Haro object

Herbig–Haro object  

A small nebula with an emission-line spectrum, found in regions of star formation. HH objects have high velocities of several hundred kilometres per second relative to their surroundings. They are ...
Russell Alan Hulse

Russell Alan Hulse  

Reference type:
Overview Page
(1950–) American astrophysicistHulse was born in New York City. He was interested in science from an early age. In 1963 he entered the Bronx High School of Science and in 1966 went to Cooper Union ...
Crab Nebula

Crab Nebula  

A supernova remnant approximately 6500 l.y. away in the constellation Taurus; also known as M1 or NGC 1952, and as the radio source Taurus A. The Crab Nebula is the remains of a star that was seen to ...
Jan Hendrik Oort

Jan Hendrik Oort  

(1900–1992)Dutchastronomer. He studied with J. C. Kapteyn, whose work on star streams he continued, finding an overall net motion of the Sun with respect to other stars. In 1927 he showed that ...
halo population

halo population   Quick reference

A Dictionary of Astronomy (3 ed.)

Reference type:
Subject Reference
Current Version:
2018

...and are believed to be older than most stars in the galactic disk, such as the Sun. Some are found within the disk but are simply in transit through it on their elongated orbits around the galactic centre, and can easily be distinguished by their high velocities with respect to the disk stars ( see high-velocity star...

Herbig–Haro object

Herbig–Haro object   Quick reference

A Dictionary of Astronomy (3 ed.)

Reference type:
Subject Reference
Current Version:
2018

...object ( HH object ) A small nebula with an emission-line spectrum, found in regions of star formation. HH objects have high velocities of several hundred kilometres per second relative to their surroundings. They are believed to be bow shocks formed when fast-flowing jets of material from a young star encounter interstellar matter. The emission lines result from the recombination of ions and electrons in the cooling gas behind the bow shock. They are named after the American George Howard Herbig ( 1920–2013 ) and the Mexican Guillermo Haro ...

Oort, Jan Hendrik

Oort, Jan Hendrik (1900–1992)   Quick reference

A Dictionary of Astronomy (3 ed.)

Reference type:
Subject Reference
Current Version:
2018

...Jan Hendrik ( 1900–1992 ) Dutch astronomer . He studied with J. C. Kapteyn , whose work on star streams he continued, finding an overall net motion of the Sun with respect to other stars. In 1927 he showed that high-velocity stars appeared to be rotating about the galactic centre, and went on to estimate the Sun’s distance from the centre and also the Galaxy’s diameter and mass. He also suggested that the Galaxy had missing mass . In the 1950s he and others (including B. J. Bok and H. van de Hulst ) used the 21-cm line of interstellar...

runaway star

runaway star   Quick reference

A Dictionary of Astronomy (3 ed.)

Reference type:
Subject Reference
Current Version:
2018

...star A young star moving at high velocity, perhaps hundreds of kilometres per second, suggesting that it has been ejected by some violent event from its birthplace. Such stars were probably once part of a binary, but were ejected either when their companion exploded as a supernova, or else through a close encounter with another binary. Examples of the first type are Zeta Ophiuchi and the pulsar PSR J1932+1059, resulting from a binary disrupted by a supernova about a million years ago. AE Aurigae and Mu Columbae, moving away from the Trapezium region of...

Crab Nebula

Crab Nebula   Quick reference

A Dictionary of Astronomy (3 ed.)

Reference type:
Subject Reference
Current Version:
2018

...source Taurus A. The Crab Nebula is the remains of a star that was seen to explode as a supernova of Type II in ad 1054 , reaching a maximum apparent magnitude of −6. In telescopes it appears as an elliptical nebulosity of 8th magnitude. Its true dimensions are 11 × 7.5 l.y. Optically, the nebula has two components: an outer region of reddish, twisted filaments of hydrogen gas; and an inner, whitish core that shows no spectral features. The light from the core is synchrotron radiation , caused by high-speed electrons from the Crab Pulsar . It is highly...

Hulse, Russell Alan

Hulse, Russell Alan   Quick reference

A Dictionary of Scientists

Reference type:
Subject Reference
Current Version:
2003
Subject:
Science and technology
Length:
357 words

...was born in New York City. He was interested in science from an early age. In 1963 he entered the Bronx High School of Science and in 1966 went to Cooper Union college in lower Manhattan. In 1974 Hulse was working as a graduate student at the University of Massachusetts, Amherst, under the supervision of Joseph Taylor . It was arranged that he would spend the summer in Puerto Rico using the Arecibo Radio Telescope to search for pulsars, a type of star first observed by Jocelyn Bell Burnell in 1967 . Among several pulsars detected by Hulse one...

supernova

supernova   Reference library

The Oxford Companion to the History of Modern Science

Reference type:
Subject Reference
Subject:
Science and technology, History of Science
Length:
619 words

...the star beyond the Chandrasekhar limit ( See Star ), triggers a wave of nuclear reactions and a flood of neutrinos, either destroying the star completely or leaving behind a neutron star. Type II results from the explosion of a young, massive giant star that has exhausted its nuclear fuel. In February 1987 a Type II supernova exploded nearby, in the Large Magellanic Cloud. The pre-nova star was a supergiant. In exploding, its brightness increased by 10 8 in a few hours. The visible energy release of 10 44 joules was dwarfed by the 10 46 joules of high...

sublight

sublight adj   Reference library

The Oxford Dictionary of Science Fiction

Reference type:
Subject Reference
Current Version:
2007

...that a part of the ship had been proceeding at hyperspeed while the rest had been slowed instantaneously to sublight velocity. 1993 SF Age (Jan.) 42/2 They ambled from star to star at sublight speeds, taking decades for each journey. 2002 A. Roberts Stone (2002) 139 When people from the Wheah made the slow sublight journey through the Tongue they—obviously—chose its narrowest point. 2 slower-than-light . 1960 P. Anderson High Crusade (1968) 37 Such dials as those for altitude and speed could readily be mastered. But what did “fuel flow”...

distance ladder

distance ladder   Reference library

The Oxford Companion to Cosmology

Reference type:
Subject Reference
Current Version:
2008
Subject:
Science and technology, Astronomy and Cosmology
Length:
1,500 words
Illustration(s):
4

...stars luminosity can only be estimated to ± ~ 0.5 mag and hence distance to ~ 25%. Photometric parallax Obtaining a high-quality spectrum for a star is quite observationally expensive and so the method of photometric parallax uses observations of the colour of a star to estimate its luminosity. This is much less accurate than the luminosity obtained from spectroscopic parallax, but one can observe the colours of many thousands of stars in a star cluster using just two or three observations and obtain a reliable estimate of the distance to the cluster. Note that...

Cepheid variables

Cepheid variables   Reference library

The Oxford Companion to Cosmology

Reference type:
Subject Reference
Current Version:
2008

...were also important in deriving the Hubble law, which states that, on average, the recession velocity of a galaxy is linearly proportional to its distance. It is now known that there are two types of Cepheid with distinct period–luminosity relations. Type I Cepheids have a high proportion of heavy elements (‘metals’) in their outer layers, and are about four times more luminous for a given period than the metal-poor Type II Cepheids. The type of a Cepheid star may be determined from its spectrum; Type I Cepheids show a large number of absorption lines...

Sun

Sun   Quick reference

A Dictionary of Astronomy (3 ed.)

Reference type:
Subject Reference
Current Version:
2018

... ( symbol ☉ ) The central body of the Solar System, and by far the nearest star to us—the only one that we can examine in great detail. It is classified as a G2V star: a yellowish star with an effective temperature of 5772 K (spectral type G2) and a main-sequence dwarf (luminosity class V). Its apparent visual magnitude is −26.7, but its absolute magnitude is only +4.82. The Sun is largely hydrogen (71% by mass), with some helium (27%) and heavier elements (total 2%). Its age is estimated to be about 4.6 billion years. The energy produced by nuclear...

Weapons

Weapons   Reference library

The Oxford Dictionary of Science Fiction

Reference type:
Subject Reference
Current Version:
2007

...weapons may also be found. Needle guns (which, confusingly, are also called needlers ) fire tiny slivers of metal at very high velocities. When both energy weapons and modern guns (i.e., ones that merely fire bullets) co-exist, the latter are often known as slugthrowers . If you don't have a gun, or find yourself in hand-to-hand combat, a vibroblade might come in handy. Vibroblades, knives or swords that vibrate at an extremely high frequency, are frequently able to cut through metal. With this kind of arsenal available, a being needs to be able to defend...

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