Messier 4
Encyclopedia
Messier 4 or M4 is a globular cluster
in the constellation
of Scorpius
. It was discovered by Philippe Loys de Chéseaux in 1746 and catalogued by Charles Messier
in 1764. It was the first globular cluster in which individual stars were resolved.
s as a fuzzy ball of light. It appears about the same size as the Moon
in the sky. It is one of the easiest globular clusters to find, being located only 1.3 degrees west of the bright star Antares
, with both objects being visible in a wide field telescope. Modestly sized telescopes will begin to resolve individual stars of which the brightest in M4 are of apparent magnitude
10.8.
in 1783. At least 43 variable star
s have been observed within M4.
M4 is approximately 7,200 light years away, the same distance as NGC 6397
, making these the two closest globular clusters to our Solar System
. It has an estimated age of 12.2 billion years.
In astronomy, the abundance of elements other than hydrogen
and helium
is called the metallicity
, and it is usually denoted by the abundance ratio of iron
to hydrogen as compared to the Sun. For this cluster, the measured abundance of iron is equal to:
This value is the logarithm
of the ratio of iron to hydrogen relative to the same ratio in the Sun. Thus the cluster has an abundance of iron equal to 8.5% of the iron abundance in the Sun. Based upon the abundance measurements, there is evidence that this cluster hosts two distinct stellar populations. Each of the populations is a group of stars that all formed at about the same time. Thus the cluster may have undergone at least two separate cycles of star formation.
The space velocity components of this cluster are (U, V, W) = km/s. It is following an orbit through the Milky Way
that has a period of and an eccentricity
of 0.80 ± 0.03. During periapsis it comes within from the Galactic core, while at apoapsis it travels out to a distance of . The orbital inclination
is at an angle of from the galactic plane, carrying it as much as above the disk. When passing through the disk, this cluster does so at distances of less than 5 kpc from the galactic nucleus. The cluster undergoes tidal shock
during each passage, which can cause the repeated shedding of stars. Thus the cluster may have been much more massive in the past.
in 1995 have revealed white dwarf
stars in M4 that are among the oldest known stars in the Milky Way Galaxy at an age of 13 billion years. One such white dwarf has been found to be a binary star
with a pulsar companion, PSR B1620-26
and a planet orbiting it with a mass of 2.5 times that of Jupiter
.
In 1987 a millisecond pulsar
was discovered in M4 with a period of 3.0 millisecond
s or about ten times faster than the Crab Pulsar
.
Globular cluster
A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is...
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....
of Scorpius
Scorpius
Scorpius, sometimes known as Scorpio, is one of the constellations of the zodiac. Its name is Latin for scorpion, and its symbol is . It lies between Libra to the west and Sagittarius to the east...
. It was discovered by Philippe Loys de Chéseaux in 1746 and catalogued by Charles Messier
Charles Messier
Charles Messier was a French astronomer most notable for publishing an astronomical catalogue consisting of deep sky objects such as nebulae and star clusters that came to be known as the 110 "Messier objects"...
in 1764. It was the first globular cluster in which individual stars were resolved.
Visibility
M4 is conspicuous in even the smallest of telescopeTelescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
s as a fuzzy ball of light. It appears about the same size as the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
in the sky. It is one of the easiest globular clusters to find, being located only 1.3 degrees west of the bright star Antares
Antares
Antares is a red supergiant star in the Milky Way galaxy and the sixteenth brightest star in the nighttime sky . Along with Aldebaran, Spica, and Regulus it is one of the four brightest stars near the ecliptic...
, with both objects being visible in a wide field telescope. Modestly sized telescopes will begin to resolve individual stars of which the brightest in M4 are of apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
10.8.
Characteristics
M4 is a rather loosely concentrated cluster of class IX and measures 75 light years across. It features a characteristic "bar" structure across its core, visible to moderate sized telescopes. The structure consists of 11th magnitude stars and is approximately 2.5' long and was first noted by William HerschelWilliam Herschel
Sir Frederick William Herschel, KH, FRS, German: Friedrich Wilhelm Herschel was a German-born British astronomer, technical expert, and composer. Born in Hanover, Wilhelm first followed his father into the Military Band of Hanover, but emigrated to Britain at age 19...
in 1783. At least 43 variable star
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
s have been observed within M4.
M4 is approximately 7,200 light years away, the same distance as NGC 6397
NGC 6397
NGC 6397 is a globular cluster in the constellation Ara. It is located about 7,200 light-years from Earth, making it one of the two nearest globular clusters to Earth...
, making these the two closest globular clusters to our Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
. It has an estimated age of 12.2 billion years.
In astronomy, the abundance of elements other than hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
and helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
is called the metallicity
Metallicity
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...
, and it is usually denoted by the abundance ratio of iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
to hydrogen as compared to the Sun. For this cluster, the measured abundance of iron is equal to:
This value is the logarithm
Logarithm
The logarithm of a number is the exponent by which another fixed value, the base, has to be raised to produce that number. For example, the logarithm of 1000 to base 10 is 3, because 1000 is 10 to the power 3: More generally, if x = by, then y is the logarithm of x to base b, and is written...
of the ratio of iron to hydrogen relative to the same ratio in the Sun. Thus the cluster has an abundance of iron equal to 8.5% of the iron abundance in the Sun. Based upon the abundance measurements, there is evidence that this cluster hosts two distinct stellar populations. Each of the populations is a group of stars that all formed at about the same time. Thus the cluster may have undergone at least two separate cycles of star formation.
The space velocity components of this cluster are (U, V, W) = km/s. It is following an orbit through the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
that has a period of and an eccentricity
Orbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
of 0.80 ± 0.03. During periapsis it comes within from the Galactic core, while at apoapsis it travels out to a distance of . The orbital inclination
Inclination
Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
is at an angle of from the galactic plane, carrying it as much as above the disk. When passing through the disk, this cluster does so at distances of less than 5 kpc from the galactic nucleus. The cluster undergoes tidal shock
Tidal shock
A tidal shock occurs when a star cluster or other distributed astronomical object passes by a large masssuch as an interstellar cloud, resulting in gravitational perturbation on a time scale that is much less than the mean time for a star to complete an orbit within the cluster. The tidal force...
during each passage, which can cause the repeated shedding of stars. Thus the cluster may have been much more massive in the past.
Notable stars
Photographs taken with the Hubble Space TelescopeHubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
in 1995 have revealed white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
stars in M4 that are among the oldest known stars in the Milky Way Galaxy at an age of 13 billion years. One such white dwarf has been found to be a binary star
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...
with a pulsar companion, PSR B1620-26
PSR B1620-26
PSR B1620-26 is a binary star system located at a distance of 3,800 parsecs in the globular cluster of Messier 4 in the constellation of Scorpius. The system is composed of a pulsar and a white dwarf...
and a planet orbiting it with a mass of 2.5 times that of Jupiter
Jupiter mass
Jupiter mass , is the unit of mass equal to the total mass of the planet Jupiter . Jupiter mass is used to describe masses of the gas giants, such as the outer planets and extrasolar planets. It is also used in describing brown dwarfs....
.
In 1987 a millisecond pulsar
Millisecond pulsar
A millisecond pulsar is a pulsar with a rotational period in the range of about 1-10 milliseconds. Millisecond pulsars have been detected in the radio, X-ray, and gamma ray portions of the electromagnetic spectrum. The origin of millisecond pulsars is still unknown...
was discovered in M4 with a period of 3.0 millisecond
Millisecond
A millisecond is a thousandth of a second.10 milliseconds are called a centisecond....
s or about ten times faster than the Crab Pulsar
Crab Pulsar
The Crab Pulsar is a relatively young neutron star. The star is the central star in the Crab Nebula, a remnant of the supernova SN 1054, which was widely observed on Earth in the year 1054...
.