Red nuggets is the nickname given to rare, unusually small galaxies packed with large amounts of red stars that were originally observed by

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...

in 2005 in the young universe. They are ancient remnants of the first massive galaxies. The environments of red nuggets are usually consistent with the general

elliptical galaxy An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the four main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work ''The Real ...

population. Most red nuggets have merged with other galaxies, but some managed to stay unscathed.

Naming

Red nuggets are not only nicknamed for their

size Size in general is the magnitude or dimensions of a thing. More specifically, ''geometrical size'' (or ''spatial size'') can refer to linear dimensions ( length, width, height, diameter, perimeter), area, or volume. Size can also be m ...

and

color Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are assoc ...

, but also for how precious the discovery is to curious

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...

s since it challenged current theories at the time the term was coined on

galaxy formation The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have ge ...

Formation of red nuggets

Red nuggets are formed from blue nuggets. Blue nuggets are early, stream fed, star-forming systems that are quenched inside-out within the inner

kiloparsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...

(kpc) and dissipatively compacted into red nuggets at their peak of gas compaction. The compaction of the blue nugget happens at an approximately constant specific star formation rate (or SFR). The quenching of the blue nugget happens at a completely constant stellar surface density. Galaxies with more

mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different eleme ...

quench earlier than galaxies with low amounts of mass because galaxies with low amounts of mass try to quench several times. The compaction happens due to a fierce period of inflow involving (mostly small) mergers and counter-rotating streams or recycled gas. It is also frequently associated with extreme disc instability. The quenching happens because of the extremely high SFR, stellar and supernova feedback, and possibly also active galactic nuclei feedback due to the high gas density in the center of the red nugget.

Star formation

Data from NASA's

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 1 ...

observing the red nuggets Mrk 1216 and PGC 032673 has shown that the central black holes suppress star formation in red nuggets with their

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...

and feed on the gas surrounding them. This brings up the intriguing question on how they could possibly be packed so densely with stars. Results show that red nuggets may have untapped stellar "fuel" to produce their unusually large number of stars. Another

theory A theory is a rational type of abstract thinking about a phenomenon, or the results of such thinking. The process of contemplative and rational thinking is often associated with such processes as observational study or research. Theories may be ...

says that red nuggets are young elliptical galaxies, therefore forming the same way they do.

Sloan Digital Sky Survey

A team led by Ivana Damjanov found over 600 red nugget candidates in the Sloan Digital Sky Survey (or SDSS) database, of which 9 were confirmed as red nuggets. These red nuggets have been missed so long because, due to their extremely small size, they look like stars in pictures. But their spectra shows what they really are. Damjanov expressed how truly amazing the discovery was when she said,

“Looking for ‘red nuggets’ in the Sloan Digital Sky Survey was like panning a riverbed, washing away silt and mud to uncover bits of gold,”

Before Damjanov and her team had thought to look through the immense database of the SDSS, no one could find the elusive galaxies after their original discovery in 2005.

References

{{Galaxy Galaxies

Naming

Formation of red nuggets

Star formation

Sloan Digital Sky Survey

See also

References