Dark galaxy: Difference between revisions
m clean up for Book:Galaxies using AWB |
m moved Dark galaxy to Dark body |
(No difference)
| |
Revision as of 14:31, 23 March 2011
A dark galaxy is a hypothetical galaxy composed of dark matter[1]. Dark galaxies receive their name because they have no detectable stars and are theoretically invisible. An influential community of scientists conjecture the existence of dark galaxies to support theories based on other well studied celestial bodies[2]. There is experimental evidence to support the existence of dark galaxies, although scientists have no conclusive evidence and continue their research. Scientists have proposed a means to track down the dark dwarf galaxies that should be orbiting the Milky Way, saying they have now found evidence of one.[3].
Observational evidence
Astronomers first suspected that there was an invisible galaxy, dark galaxy, out there when they spied galaxy NGC 4254. This unusual-looking galaxy appears to be one partner in a cosmic collision. The only evidence is the following: gas is being siphoned away into a tenuous stream, and one of its spiral arms is being stretched out. The other partner in this collision is nowhere to be seen. The researchers calculated that an object with 100 billion solar masses theoretically careened past NGC 4254 within the last 100 million years creating the gas stream and tearing at one of its arms. This was the clue that an invisible dark matter galaxy might be lurking nearby[4].
Nature of dark galaxy
Origin
In 2000 astronomers found a gas cloud VIRGOHI21 and tried to find a theory of what it was and or why it could cause such a gravitational pull from NGC 4254 galaxy. After years of running out of other explanations some have concluded that VIRGOHI21 is a dark galaxy, due to the massive effect it had on NGC 4254[1].
Size
The actual size of a dark galaxy is unknown, because they cannot be spotted with a normal telescope. There have been various estimations of the size of dark galaxies. Two potential sizes could be either double the size of the Milky Way[4] or the size of a small quasar.
Structure
Dark galaxies are composed of dark matter. Furthermore, dark galaxies are theoretically composed of hydrogen and dust[1]. Some scientists support the idea that dark galaxies may contain stars[3]. Yet the exact composition of dark galaxies is unknown because there is no conclusive way to spot them so far.
Methodology to observe dark bodies
Dark galaxies contain no visible stars, and are not visible through conventional methods, i.e. telescopes. Arecibo Galaxy Environment Survey (AGES) a current study using the Arecibo radio telescope to search for dark galaxies. The Arecibo radio telescope is useful where others are not because of its ability to detect neutral-hydrogen wavelengths[5].
Alternative theories
Scientists do not have much explanation for some astronomic events, so some use the idea of a dark galaxy to explain these events. Little is known about dark galaxies, and some scientists believe dark galaxy is actually a newly forming galaxy. One such candidate is in the Virgo cluster. This candidate contains very few stars. Scientist classify this galaxy as a newly forming galaxy, rather than a dark galaxy.[6].
Potential dark galaxies
HE0450-2958
HE0450-2958 is an unusual quasar (a star like object that may send out radio waves and other forms of energy). This one in particular has many large red shifts[7]. HE0450-2958 has no visible host galaxy (a galaxy surrounding the quasar) detected around it. It has been suggested that this may be a dark galaxy in which a quasar has become active. However subsequent observations revealed that a normal host galaxy is probably present[8].
HVC 127-41-330
HVC 127-41-330 is a cloud at high speed between the Andromeda and the Triangulum Galaxy. Astronomer Josh Simon considers this cloud to be a dark galaxy because of the speed of its rotation and its predicted mass[9].
VIRGOHI21
The discovery of VIRGOHI21 was announced in February 2005, and it was the first good candidate to be a true dark galaxy[2][3][10][11]. It was found when AGES was looking for the 21 cm-wavelength radio waves emitted by hydrogen (H). Its dynamics are apparently inconsistent with the predictions of the Modified Newtonian Dynamics (MOND) theory[12]. Some researchers have since discounted the possibility of VIRGOHI21 being a dark galaxy and believe it is more likely a "tidal tail"[13]. of nearby galaxy NGC 4254, which is experiencing gravitational perturbations as it enters the Virgo cluster
See also
References
- ^ a b c http://www.universetoday.com/1888/no-stars-shine-in-this-dark-galaxy/
- ^ a b Clark, Stuart (2005-02-23). "Astronomers claim first 'dark galaxy' find". NewScientist.com news service. Retrieved 2006-10-26.
- ^ a b c Stuart Clark. "Dark galaxy' continues to puzzle astronomers". New Scientist. Retrieved 2008-02-26.
- ^ a b http://www.spacedaily.com/reports/Arecibo_Survey_Produces_Dark_Galaxy_Candidate.html
- ^ http://www.dailygalaxy.com/my_weblog/2009/12/darkmatter-galaxy-ten-billion-xs-the-mass-of-the-sun.html
- ^ http://newsblaze.com/story/20091130170354drex.nb/topstory.html
- ^ Magain, P. et al. (2005), Discovery of a bright quasar without a massive host galaxy, Nature, 437, 381
- ^ Merritt, D. et al. (2005), The nature of the HE0450-2958 System, arXiv:astro-ph/0511315
- ^ Josh Simon (2005). "Dark Matter in Dwarf Galaxies: Observational Tests of the Cold Dark Matter Paradigm on Small Scales" (PDF).
{{cite journal}}: Cite journal requires|journal=(help) - ^ Shiga, David (2005-02-26). "Ghostly Galaxy: Massive, dark cloud intrigues scientists". Science News Online. 167 (9). Society for Science &: 131. doi:10.2307/4015891. JSTOR 10.2307/4015891. Retrieved 2008-09-14.
- ^ Britt, Roy (2005-02-23). "First Invisible Galaxy Discovered in Cosmology Breakthrough". Space.com.
- ^ Funkhouser, Scott (2005). "Testing MOND with VirgoHI21". Monthly Notices of the Royal Astronomical Society. 364: 237. arXiv:astro-ph/0503104. doi:10.1111/j.1365-2966.2005.09565.x.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ Haynes, Martha P.; Giovanelli, Riccardo; Kent, Brian R. (2007). "NGC 4254: An Act of Harassment Uncovered by the Arecibo Legacy Fast ALFA Survey". Astrophysical Journal. 665 (1): L19–22. doi:10.1086/521188.
{{cite journal}}: CS1 maint: multiple names: authors list (link)
- Battersby, Stephen (2003-10-20). "Astronomers find first 'dark galaxy'". New Scientist.
External links
- Universe Today, Some Galaxies Are Made Almost Entirely of Dark Matter
