Messier 4

Use the bright star, Antares, to help you find Messier 4.

Distance

5,500 light-years

Apparent Magnitude

5.9

constellation

Scorpius

object type

Globular Cluster

This sparkling picture taken by the NASA/ESA Hubble Space Telescope shows the centre of globular cluster M 4. The power of Hubble has resolved the cluster into a multitude of glowing orbs, each a colossal nuclear furnace. M 4 is relatively close to us, lying 7200 light-years distant, making it a prime object for study. It contains several tens of thousand stars and is noteworthy in being home to many white dwarfs — the cores of ancient, dying stars whose outer layers have drifted away into space. In July 2003, Hubble helped make the astounding discovery of a planet called PSR B1620-26 b, 2.5 times the mass of Jupiter, which is located in this cluster. Its age is estimated to be around 13 billion years — almost three times as old as the Solar System! It is also unusual in that it orbits a binary system of a white dwarf and a pulsar (a type of neutron star). Amateur stargazers may like to track M 4 down in the night sky. Use binoculars or a small telescope to scan the skies near the orange-red star Antares in Scorpius. M 4 is bright for a globular cluster, but it won’t look anything like Hubble’s detailed image: it will appear as a fuzzy ball of light in your eyepiece. On Wednesday 5 September, the European Southern Observatory (ESO) will publish a wide-field image of M 4, showing the full spheroidal shape of the globular cluster. See it at www.eso.org on Wednesday.

ESA/Hubble & NASA

M4, located in the constellation Scorpius, is a huge, spherical collection of stars known as a globular cluster. Just 5,500 light-years away, it is the closest globular cluster to Earth. Because of its apparent magnitude of 5.9 and proximity to Antares, one of the brightest stars in the night sky, M4 is relatively easy to find with a small telescope. The cluster is best spotted in July.

In order to capture M4’s oldest white dwarfs, Hubble took many snapshots of the cluster in infrared, visible and ultraviolet light, which were combined into this image of a small portion of the cluster. These observations amounted to nearly eight days of exposure time over a 67-day period.

NASA and H. Richer (University of British Columbia)

M4 was discovered in 1746 by the Swiss astronomer Jean-Philippe Loys de Chéseaux. Home to more than 100,000 stars, the cluster is predicted to contain up to 40,000 white dwarfs — the cores of ancient, dead stars whose outer layers have drifted away into space. As white dwarfs age, they grow cooler, fainter, and more difficult to detect. Therefore, a globular cluster’s age can be inferred from the age of its faintest white dwarf. Because the stars in these clusters are some of the oldest in the universe, up to 13 billion years old, astronomers are able to use them to estimate the age of the universe.

The white dwarfs in M4 are less than one-billionth the apparent brightness of the faintest stars that can be seen with the naked eye. Even the brightest of the detected white dwarfs are no more luminous than a 100-watt light bulb seen at the moon’s distance. The faintest are comparable to a 2.5-watt night-light at the same distance.

The ancient orbs comprising M4 were captured by Hubble in both visible and infrared light. The resulting image offers a view into the center of a cluster that is more than twice the age of our solar system.

This video begins with a ground-based view of a region of the sky near Scorpius and zooms into a detailed Hubble image of M4. Some of the faint white dwarfs Hubble observed are circled in blue to differentiate them from the red giants that dominate the field.
NASA and B. Preston (STScI and Max-Q Digital)

For more information about Hubble’s observations of M4, see:

This star chart for M4 represents the view from mid-northern latitudes for the given month and time.

Image courtesy of Stellarium

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