Information:  - A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. The word galaxy is derived from the Greek "", literally "milky", a reference to the Milky Way. Galaxies range in size from dwarfs with just a few billion stars to giants with one hundred trillion stars, each orbiting its galaxy's center of mass. Galaxies are categorized according to their visual morphology as elliptical, spiral and irregular. Many galaxies are thought to have black holes at their active centers. The Milky Way's central black hole, known as Sagittarius A*, has a mass four million times greater than the Sun. As of March 2016, GN-z11 is the oldest and most distant observed galaxy with a comoving distance of 32 billion light-years from Earth, and observed as it existed just 400 million years after the Big Bang.  - X-radiation (composed of X-rays) is a form of electromagnetic radiation. Most X-rays have a wavelength ranging from 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3×10 Hz to 3×10 Hz) and energies in the range 100 eV to 100 keV. X-ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays. In many languages, X-radiation is referred to with terms meaning Röntgen radiation, after the German (German-Dutch to be precise) scientist Wilhelm Röntgen, who usually is credited as its discoverer, and who had named it "X-radiation" to signify an unknown type of radiation. Spelling of "X-ray(s)" in the English language includes the variants "x-ray(s)", "xray(s)", and "X ray(s)".  - A brightest cluster galaxy (BCG) is defined as the brightest galaxy in a cluster of galaxies. BCGs include the most massive galaxies in the universe. They are generally elliptical galaxies which lie close to the geometric and kinematical center of their host galaxy cluster, hence at the bottom of the cluster potential well. They are also generally coincident with the peak of the cluster X-ray emission.  - A light-year is a unit of length used to express astronomical distances. It is about 9 trillion kilometres or 6 trillion miles. As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in vacuum in one Julian year (365.25 days). Because it includes the word "year", the term light-year is sometimes misinterpreted as a unit of time.  - A potential well is the region surrounding a local minimum of potential energy. Energy captured in a potential well is unable to convert to another type of energy (kinetic energy in the case of a gravitational potential well) because it is captured in the local minimum of a potential well. Therefore, a body may not proceed to the global minimum of potential energy, as it would naturally tend to due to entropy.  - The Universe is all of time and space and its contents. It includes planets, moons, minor planets, stars, galaxies, the contents of intergalactic space, and all matter and energy. The size of the entire Universe is unknown.  - IC 1101 is a supergiant elliptical galaxy at the center of the Abell 2029 galaxy cluster, approximately 320 megaparsecs (1.04 billion light-years) from Earth.  - A galaxy cluster, or cluster of galaxies, is a structure that consists of anywhere from hundreds to thousands of galaxies that are bound together by gravity with typical masses ranging from 1010 solar masses. They are the largest known gravitationally bound structures in the universe and were believed to be the largest known structures in the universe until the 1980s, when superclusters were discovered. One of the key features of clusters is the intracluster medium (ICM). The ICM consists of heated gas between the galaxies and has a peak temperature between 215 keV that is dependent on the total mass of the cluster. Galaxy clusters should not be confused with star clusters, such as open clusters, which are structures of stars "within" galaxies, or with globular clusters, which typically orbit galaxies. Small aggregates of galaxies are referred to as groups of galaxies rather than clusters of galaxies. The groups and clusters can themselves cluster together to form superclusters.  - An elliptical galaxy is a type of galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. Unlike flat spiral galaxies with organization and structure, they are more three-dimensional, without much structure, and their stars are in somewhat random orbits around the center. They are one of the three main classes of galaxy originally described by Edwin Hubble in his 1936 work "The Realm of the Nebulae", along with spiral and lenticular galaxies. Elliptical galaxies range in shape from nearly spherical to highly flat and in size from tens of millions to over one hundred trillion stars. Originally Edwin Hubble hypothesized that elliptical galaxies evolved into spiral galaxies, which was later discovered to be false. Stars found inside of elliptical galaxies are much older than stars found in spiral galaxies.  - Abell 2029 or A2029 is a large cluster of galaxies 315 megaparsecs ( 1,027 million light - years ) away in the constellation Virgo . A2029 is a Bautz - Morgan classification type I cluster due to its large central galaxy , IC 1101 . This type of galaxy is called a cD - type brightest cluster galaxy and may have grown to its large size by accreting nearby galaxies .    Given the information above, choose from the list below the object entity that exhibits the relation 'instance of' with the subject 'abell 2029'.  Choices: - 1  - case  - classification  - cluster  - constellation  - dark matter  - distance  - electromagnetic radiation  - galaxy  - galaxy cluster  - language  - march  - mass  - may  - morphology  - orbit  - range  - region  - size  - space  - star  - state  - structure  - temperature  - term  - three  - time  - union  - unit of time  - word  - year
Answer:
galaxy cluster