MACHO-1997-BLG-41
Encyclopedia
MACHO-1997-BLG-41, commonly abbreviated as 97-BLG-41 or MACHO-97-BLG-41, was a gravitational microlensing
event located in Sagittarius
which occurred in July 1999. The source star is likely a giant
or subgiant star of spectral type
K located at a distance of around 8 kiloparsecs
(26,000 light years). The lens star is a binary system
approximately 10,000 light years away in the constellation
Sagittarius
. The two star
s are separated from each other by about 0.9 AU
and have an orbital period of around 1.5 years. The most likely mass of the system is about 0.3 times that of our Sun
. Star A and star B are both red dwarf
s.
The first published model of the MACHO-1997-BLG-41 event gave the lens system as being located in the galactic bulge at a distance of 6.3 kiloparsec
s (21,000 light years), a total system mass of about 0.8 times that of the Sun
and a separation of 1.8 AU
(the most likely value given a random orientation of the system). The individual components were assigned masses 0.6 and 0.16 times that of our Sun
, making them an orange dwarf
of spectral class K and a class M red dwarf
respectively. According to this model, a planet with around 3.5 times the mass
of Jupiter
orbits in a circumbinary orbit around the two stars at a distance of around 7 AU (assuming random orientation of the system).
Subsequently, an independent analysis of another team revealed that the microlensing event could be interpreted as being caused by a low-mass binary system of two red dwarf
stars located in the galactic disk if one considers their orbital motion, without the need to invoke a planetary mass. The planet is thus considered disproven.
Gravitational microlensing
Gravitational microlensing is an astronomical phenomenon due to the gravitational lens effect. It can be used to detect objects ranging from the mass of a planet to the mass of a star, regardless of the light they emit. Typically, astronomers can only detect bright objects that emit lots of light ...
event located in Sagittarius
Sagittarius (constellation)
Sagittarius is a constellation of the zodiac, the one containing the galactic center. Its name is Latin for the archer, and its symbol is , a stylized arrow. Sagittarius is commonly represented as a centaur drawing a bow...
which occurred in July 1999. The source star is likely a giant
Giant star
A giant star is a star with substantially larger radius and luminosity than a main sequence star of the same surface temperature. Typically, giant stars have radii between 10 and 100 solar radii and luminosities between 10 and 1,000 times that of the Sun. Stars still more luminous than giants are...
or subgiant star of spectral type
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
K located at a distance of around 8 kiloparsecs
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
(26,000 light years). The lens star is a binary system
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
approximately 10,000 light years away in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Sagittarius
Sagittarius (constellation)
Sagittarius is a constellation of the zodiac, the one containing the galactic center. Its name is Latin for the archer, and its symbol is , a stylized arrow. Sagittarius is commonly represented as a centaur drawing a bow...
. The two star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s are separated from each other by about 0.9 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
and have an orbital period of around 1.5 years. The most likely mass of the system is about 0.3 times that of our Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. Star A and star B are both red dwarf
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
s.
The first published model of the MACHO-1997-BLG-41 event gave the lens system as being located in the galactic bulge at a distance of 6.3 kiloparsec
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
s (21,000 light years), a total system mass of about 0.8 times that of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
and a separation of 1.8 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
(the most likely value given a random orientation of the system). The individual components were assigned masses 0.6 and 0.16 times that of our Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, making them an orange dwarf
Orange dwarf
A K-type main-sequence star , also referred to orange dwarf, are main-sequence stars of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars and yellow G-type main-sequence stars...
of spectral class K and a class M red dwarf
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
respectively. According to this model, a planet with around 3.5 times the mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
orbits in a circumbinary orbit around the two stars at a distance of around 7 AU (assuming random orientation of the system).
Subsequently, an independent analysis of another team revealed that the microlensing event could be interpreted as being caused by a low-mass binary system of two red dwarf
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
stars located in the galactic disk if one considers their orbital motion, without the need to invoke a planetary mass. The planet is thus considered disproven.