The Cloverleaf quasar (H1413+117, QSO J1415+1129) is a bright, gravitationally lensed

quasar A quasar is an extremely luminous active galactic nucleus (AGN). It is pronounced , and sometimes known as a quasi-stellar object, abbreviated QSO. This emission from a galaxy nucleus is powered by a supermassive black hole with a mass rangin ...

Quasar

Molecular gas (notably CO) detected in the host galaxy associated with the quasar is the oldest molecular material known and provides evidence of large-scale star formation in the early universe. Thanks to the strong magnification provided by the foreground

lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements'' ...

, the Cloverleaf is the brightest known source of CO emission at high redshift and was also the first source at a

redshift In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and simultaneous increase in f ...

to be detected with HCN or HCO⁺ emission. The 4 quasar images were originally discovered in 1984; in 1988, they were determined to be a single quasar split into four images, instead of 4 separate quasars. The

X-rays X-rays (or rarely, ''X-radiation'') are a form of high-energy electromagnetic radiation. In many languages, it is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it in 1895 and named it ' ...

from iron atoms were also enhanced relative to X-rays at lower energies. Since the amount of brightening due to gravitational lensing doesn't vary with the wavelength, this means that an additional object has magnified the X-rays. The increased

magnification Magnification is the process of enlarging the apparent size, not physical size, of something. This enlargement is quantified by a calculated number also called "magnification". When this number is less than one, it refers to a reduction in si ...

of the X-ray light can be explained by gravitational

microlensing Gravitational microlensing is an astronomical phenomenon due to the gravitational lens effect. It can be used to detect objects that range from the mass of a planet to the mass of a star, regardless of the light they emit. Typically, astronomers ...

, an effect which has been used to search for compact

stars A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

and

planets A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a young ...

in our galaxy. Microlensing occurs when a star or a multiple star system passes in front of light from a background object. If a single star or a multiple star system in one of the foreground galaxies passed in front of the light path for the brightest image, then that image would be selectively magnified.

Black hole

The X-rays would be magnified much more than the

visible light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 tera ...

if they came from a region around the central

supermassive black hole A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions of times the mass of the Sun (). Black holes are a class of astronomical obj ...

of the lensing galaxy that was smaller than the origin region of the visible light. The enhancement of the

from

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...

ions An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

would be due to this same effect. The analysis indicates that the X-rays are coming from a very small region, about the size of the

Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

, around the central black hole. The visible light is coming from a region ten or more times larger. The angular size of these regions at a distance of 11 billion

light years A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

is tens of thousands times smaller than the smallest region that can be resolved by the Hubble Space

Telescope A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to obse ...

. This provides a way to test models for the flow of gas around a supermassive black hole.

Lensing galaxy and partial Einstein ring

Data from NICMOS and a special

algorithm In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific problems or to perform a computation. Algorithms are used as specifications for performing ...

resolved the lensing galaxy and a partial

Einstein ring An Einstein ring, also known as an Einstein–Chwolson ring or Chwolson ring (named for Orest Chwolson), is created when light from a galaxy or star passes by a massive object en route to the Earth. Due to gravitational lensing, the light is dive ...

. The Einstein ring represents the host galaxy of the lensed quasar.

History

The Cloverleaf quasar was discovered in 1988. Data on the Cloverleaf collected by the

Chandra X-ray Observatory The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space telescope launched aboard the during STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources ...

in 2004 were compared with that gathered by optical telescopes. One of the X-ray components (A) in the Cloverleaf is brighter than the others in both optical and X-ray light but was found to be relatively brighter in X-ray than in optical light. The X-rays from iron atoms were also enhanced relative to X-rays at lower energies.

References

External links

* Chandra at Havard CfA
"Cloverleaf Quasar: Chandra Looks Over a Cosmic Four-Leaf Clover"
20 February 2009 {{DEFAULTSORT:Cloverleaf Quasar Gravitationally lensed quasars Boötes