HL Tauri (abbreviated HL Tau) is a young

T Tauri star T Tauri stars (TTS) are a class of variable stars that are less than about ten million years old. This class is named after the prototype, T Tauri, a young star in the Taurus Molecular Cloud, Taurus star-forming region. They are found near mo ...

in the constellation

Taurus Taurus is Latin for 'bull' and may refer to: * Taurus (astrology), the astrological sign ** Vṛṣabha, in vedic astrology * Taurus (constellation), one of the constellations of the zodiac * Taurus (mythology), one of two Greek mythological ch ...

, approximately from

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

in the Taurus Molecular Cloud. The

luminosity Luminosity is an absolute measure of radiated electromagnetic radiation, electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electroma ...

and

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of imply that its age is less than 100,000 years. At

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

15.1, it is too faint to be seen with the unaided eye. It is surrounded by a

protoplanetary disk A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may not be considered an accretion disk; while the two are sim ...

marked by dark bands visible in

submillimeter radiation Terahertz radiation – also known as submillimeter radiation, terahertz waves, tremendously high frequency (THF), T-rays, T-waves, T-light, T-lux or THz – consists of electromagnetic waves within the International Telecommunicat ...

that may indicate a number of

planets A planet is a large, rounded astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets by the most restrictive definition of the te ...

in the process of

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondary ...

. It is accompanied by the

Herbig–Haro object Herbig–Haro (HH) objects are bright patches of nebula, nebulosity associated with newborn stars. They are formed when narrow jets of partially plasma (physics), ionised gas ejected by stars collide with nearby clouds of gas and dust at several ...

, a jet of gas emitted along the rotational axis of the disk that is colliding with nearby interstellar dust and gas.

Protoplanetary disk

Indications of a

were first presented in 1975 with

infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

spectral observations in

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

s between 2 and 4

micron The micrometre (English in the Commonwealth of Nations, Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a uni ...

s, which were made possible by the recent invention of the

indium antimonide Indium antimonide (InSb) is a crystalline compound made from the elements indium (In) and antimony (Sb). It is a narrow- gap semiconductor material from the III- V group used in infrared detectors, including thermal imaging cameras, FLIR sy ...

photovoltaic detector. Of 29 very young stars examined, only showed a strong absorption feature centered on the expected 3.07 micron absorption of ice particles, which authors attributed to the ν₁, ν₃, and 2ν₂ vibrational frequencies of the O– H bond. A 1982 survey identified as one of the most highly polarized stars known, along with

DG Tauri DG Tauri is a young star about 400 light years from the Earth. It is a T Tauri-type variable star, ranging in brightness from magnitude 10.5 to 14.9 (in blue light), making it far too faint to be seen with the naked eye. DG Tauri is lo ...

and V536 Aquilae. A gas disk was discovered by interferometric observation of

carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

(CO) emissions in 1986. Based on observation data in 1985 and 1986 from the Millimeter Wave Interferometer of the

Owens Valley Radio Observatory Owens Valley Radio Observatory (OVRO) is a radio astronomy observatory located near Big Pine, California (US) in Owens Valley. It lies east of the Sierra Nevada, approximately north of Los Angeles and southeast of Bishop. It was established in 19 ...

, the circumstellar disk was estimated to have a mass between and , with a best fit of , and a radius of about 200 AU. The temperature of the gas and grains of the disk are probably of the order of a few tens of

kelvin The kelvin (symbol: K) is the base unit for temperature in the International System of Units (SI). The Kelvin scale is an absolute temperature scale that starts at the lowest possible temperature (absolute zero), taken to be 0 K. By de ...

s. The gas was found to be bound to and in Keplerian rotation around a star with a mass of about .

Bipolar outflow A bipolar outflow comprises two continuous flows of gas from the poles of a star. Bipolar outflows may be associated with protostars (young, forming stars), or with evolved post-AGB stars (often in the form of bipolar nebulae). Protostars I ...

of molecules such as carbon monoxide (CO) and diatomic hydrogen (H₂) have been observed. The element

iron Iron is a chemical element; it has symbol Fe () 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, forming much of Earth's o ...

has also been noted in the outflow in its Fe(II) oxidation state, also called Fe²⁺ or ''ferrous iron''. An image of the protoplanetary disk made at submillimeter wavelengths by the

Atacama Large Millimeter/submillimeter Array The Atacama Large Millimeter/submillimeter Array (ALMA) is an astronomical interferometer of 66 radio telescopes in the Atacama Desert of northern Chile, which observe electromagnetic radiation at millimeter and submillimeter wavelengths. The arr ...

(ALMA) was made public in 2014, showing a series of concentric bright rings separated by gaps. The disk appeared much more evolved than would have been expected from the age of the system, which suggests that the planetary formation process may be faster than previously thought. ALMA's Catherine Vlahakis said, "When we first saw this image we were astounded at the spectacular level of detail. HL Tauri is no more than a million years old, yet already its disk appears to be full of forming planets. This one image alone will revolutionize theories of

planet formation The nebular hypothesis is the most widely accepted model in the field of cosmogony to explain the formation and evolution of the Solar System (as well as other planetary systems). It suggests the Solar System is formed from gas and dust orbiting t ...

." Stephens ''et al.'' (2014) suggest that the faster accretion rate might be due to the complex magnetic field of the protoplanetary disk. In 2024, water was found within the protoplanetary disk using the Atacama Large Millimeter Array (ALMA), containing 3.7 Earth oceans worth of water vapour.

Gallery

A glowing jet from a young star.tif, A wider view of the region (HL Tauri out of frame at bottom right corner) from the

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

in visible light shows the

. Heic1424a.tif, A broader view of the Taurus Molecular Cloud region. is shrouded in the bright blue region at upper center-left. HLTauLightCurve.png, A visual band

light curve In astronomy, a light curve is a graph (discrete mathematics), graph of the Radiance, light intensity of a celestial object or region as a function of time, typically with the magnitude (astronomy), magnitude of light received on the ''y''-axis ...

for HL Tauri, plotted from ''

ASAS-SN The All Sky Automated Survey for SuperNovae (ASAS-SN) is an automated program to search for new supernovae and other astronomical transients, headed by astronomers from the Ohio State University, including Christopher Kochanek and Krzysztof Stan ...

'' data

References

External links

* {{DEFAULTSORT:HL Tauri K-type stars Tauri, HL T Tauri stars Taurus (constellation) Circumstellar disks