Mira B, also known as VZ Ceti, is the companion

star 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 ...

to the

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as ...

Mira Mira (), designation Omicron Ceti (ο Ceti, abbreviated Omicron Cet, ο Cet), is a red-giant star estimated to be 200–400 light-years from the Sun in the constellation Cetus. ο Ceti is a binary stellar system, consisting of a varia ...

, separated by around . Suspected as early as 1918, it was visually confirmed in 1923 by

Robert Grant Aitken Robert Grant Aitken (December 31, 1864 – October 29, 1951) was an American astronomer. Early life and education Robert Grant Aitken was born in Jackson, California, to Scottish immigrant Robert Aitken and Wilhelmina Depinau. Aitken atten ...

, and has been observed more or less continually since then, most recently 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 1 ...

. Long known to be erratically variable itself, its fluctuations seem to be related to its accretion of

matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic partic ...

from Mira's stellar wind, which makes it a symbiotic star.

Orbit

Its

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

around Mira is poorly known; the most recent estimate listed in the Sixth Catalog of Orbits of Visual Binary Stars gives an

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

of roughly 500 years, with a

periastron An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any elli ...

around the year 2285. Assuming the distance in the ''

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...

'' catalog and orbit are correct, Mira A and B are separated by an average of 100 AU.

Current research

In January 2007, astronomers at the

Keck Observatory The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and when co ...

announced the discovery of 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 also be considered an accretion disk for the star itself, be ...

around Mira B. Discovered via

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

data, the disk is apparently derived from captured material from Mira itself; Mira B accretes as much as one percent of the matter lost by its primary. Though planetary formation is perhaps unlikely as long as the disk is in active accretion, it may proceed apace once Mira A completes its

red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around or ...

phase and becomes a

white dwarf A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes fro ...

remnant. Several factors, such as low x-ray luminosity, suggest that Mira B is actually a normal

main-sequence star In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hert ...

spectral type In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

K and roughly 0.7

solar mass The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...

, rather than a

as first envisioned. However, a 2010 analysis of rapid optical brightness variations has indicated that Mira B is, in fact, a white dwarf.

External links

From the AAVSO Variable Star of the Month: MiraChandra Photo Album, Mira press release

Born Again Protoplanetary Disk Around Mira B

References

{{Stars of Cetus Binary stars White dwarfs Cetus (constellation) Ceti, Omicron, B Ceti, VZ Astronomical objects discovered in 1923