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White Dwarf Star Yields Key to Planet’s Mass
Three unlikely companions - two burned-out stars and a planet - orbit each other near the crowded core of an ancient globular cluster of more than 100,000 stars. Only one companion, however, is visible in the images. In the image at right, taken by NASA's Hubble Space Telescope, the white arrow points to a burned-out white dwarf star. Radio astronomers discovered the white dwarf and the other burned-out star - a rapidly spinning neutron star, called a pulsar - a decade ago. The third companion's identity was a mystery. Was it a planet or a brown dwarf? The object was too small and too dim to image.
Hubble observations of the dim white dwarf helped astronomers to precisely measure the mass of the mystery object (2.5 times larger than the mass of Jupiter), confirming that it is a planet. In fact, it is the farthest and oldest known planet. Hubble's Wide Field and Planetary Camera 2 resolved individual stars near M4's densely packed core [right] and pinpointed the white dwarf.
The image at left, taken by the National Optical Astronomy Observatory, shows the companions' home, a 13-billion-year-old cluster called M4. The green box marks the location of Hubble's close-up view.
The Hubble observations of the white dwarf held the key to discovering the identity of the third companion. Astronomers used Hubble to measure the white dwarf's color and temperature. By knowing those physical properties, astronomers then calculated the white dwarf's age and mass. They then compared that information to the amount of wobble in the pulsar signal, which allowed astronomers to calculate the tilt of the white dwarf's orbit as seen from Earth. That critical piece of evidence, when combined with the radio studies of the wobbling pulsar, allowed astronomers to determine the tilt of the planet's orbit and subsequently its mass.
The cluster is located 5,600 light-years away in the summer constellation Scorpius. The Hubble image was taken in April 1996.
About the Object
- R.A. PositionR.A. PositionRight ascension – analogous to longitude – is one component of an object's position.16h 23m 35.4s
- Dec. PositionDec. PositionDeclination – analogous to latitude – is one component of an object's position.-26° 31' 31.9"
- ConstellationConstellationOne of 88 recognized regions of the celestial sphere in which the object appears.Scorpius
- DistanceDistanceThe physical distance from Earth to the astronomical object. Distances within our solar system are usually measured in Astronomical Units (AU). Distances between stars are usually measured in light-years. Interstellar distances can also be measured in parsecs.M4 is roughly 5,600 light-years (1,720 parsecs) from the Earth.
About the Data
- Data DescriptionData DescriptionProposal: A description of the observations, their scientific justification, and the links to the data available in the science archive.
Science Team: The astronomers who planned the observations and analyzed the data. "PI" refers to the Principal Investigator.Hubble data for this release was taken from HST proposals 5461 and 8679 together with archived observations from HST proposal 8153. The full team involved in this discovery is composed of Brad Hansen (UCLA), Harvey Richer (UBC), Steinn Sigurdsson (Penn State), Ingrid Stairs (UBC) and Stephen Thorsett (UCSC). - InstrumentInstrumentThe science instrument used to produce the data.NOAO (left) and HST>WFPC2 (right)
- Exposure DatesExposure DatesThe date(s) that the telescope made its observations and the total exposure time.February - April 1995; January - April 2001 (HST mage)
- FiltersFiltersThe camera filters that were used in the science observations.HST: F336W (B) 11,800 sec, F555W (V) 15,000 sec, and F814W (I) 4800 sec
- Object NameObject NameA name or catalog number that astronomers use to identify an astronomical object.B1620-26, M4, Messier 4, NGC 6121
- Object DescriptionObject DescriptionThe type of astronomical object.Globular Cluster and Pulsar with Companion
- Release DateJuly 10, 2003
- Science ReleaseOldest Known Planet Identified
- Credits
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Claire Andreoli
NASA’s Goddard Space Flight Center
Greenbelt, Maryland
claire.andreoli@nasa.gov
