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Hubble Measures Deflection of Starlight by a Foreground Object (Artist’s Illustration)

Diagram titled “Hubble measures deflection of starlight by a foreground object.” Diagram includes an artist's illustration of the Hubble Space Telescope observing a distant star whose light curves around another object—a white dwarf star—in the foreground. The diagram shows the real position of the observed star, the light path of that star, and the apparent (“observed”) position of the star. The white dwarf is in the center of the diagram, on a grid that appears to be warped downward under the enormous mass of the white dwarf. Hubble is toward the lower right on the diagram, at the 5 o’clock position relative to the white dwarf. It is pointing up toward the 12 o’clock position, where the star appears to be (“observed star position”). A straight dashed line connects the observed star position with the telescope. The real star position is at 11 o’clock. A solid line curves from the real star position, around the white dwarf, to the telescope.

This artist's illustration shows how the gravity of a foreground white dwarf star warps space and bends the light of a distant star behind it. Astronomers using NASA's Hubble Space Telescope have for the first time directly measured the mass of a single, isolated white dwarf (the surviving core of a burned-out Sun-like star) – due to this optical trick of nature. The greater the temporary, infinitesimal deflection of the background star's image, the more massive the foreground star is. (This deviation is so small that it is equivalent to observing an ant crawl across the surface of a quarter from 1,500 miles away.) Researchers found that the dwarf is 56 percent the mass of our Sun.

This effect, called gravitational lensing was predicted as a consequence of Einstein's theory of general relativity from a century ago. Observations of a solar eclipse in 1919 provided the first experimental proof for general relativity. But Einstein didn't think the same experiment could be done for stars beyond our Sun because of the extraordinary precision required.

About the Object

  • R.A. Position
    R.A. PositionRight ascension – analogous to longitude – is one component of an object's position.
    11:45:42.9205
  • Dec. Position
    Dec. PositionDeclination – analogous to latitude – is one component of an object's position.
    -64:50:29.459
  • Constellation
    ConstellationOne of 88 recognized regions of the celestial sphere in which the object appears.
    Musca
  • Distance
    DistanceThe 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.
    About 15 light-years

About the Data

  • Data Description
    Data 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.

  • Object Name
    Object NameA name or catalog number that astronomers use to identify an astronomical object.
    LAWD 37 (LP 145-141)
  • Object Description
    Object DescriptionThe type of astronomical object.
    Isolated White Dwarf
  • Release Date
    February 2, 2023
  • Science Release
    For the First Time Hubble Directly Measures Mass of a Lone White Dwarf
    Read the release
  • Credit
    NASA, ESA, Ann Feild (STScI)

Downloads

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  • Full Res (For Print), 4250 × 3117
    tif (37.93 MB)
  • 2000 × 1467
    png (1.77 MB)

Related Images & Videos

A field of dark space scattered with numerous small points of light, with a relatively large and bright blue-white star in the center. The star has Hubble’s characteristic cross-shaped diffraction pattern. To the upper left, just within the blue-white glow of the star, is a much smaller white dot. To the upper right of the large star is a rectangular zoom-in showing the middle third of the large star, labeled “LAWD 37,” along with the smaller white circle labeled “background star.” The zoom-in also includes a curvy blue line that begins on the right near the middle of the large star LAWD 37 and ends near the lower left of the box. The curvy blue line is labeled “path of LAWD 37.” Along the path are nine small solid red squares marking the relative location of LAWD 37 with respect to the background star at nine different points in time. The squares are not evenly spaced along the line. There is a cluster just below the background star.

Hubble Observations Used to Measure Mass of Lone White Dwarf Star LAWD 37

This graphic shows how microlensing was used to measure the mass of a white dwarf star. The dwarf, called LAWD 37, is a burned-out star in the center of this Hubble Space Telescope image. Though its nuclear fusion furnace has shut down, trapped heat is sizzling on the surface at...

Image titled “LAWD 37; May 1, 2019; HST WFC3/UVIS” with a color key, a scale bar, and compass arrows. The image shows a bright blue-white star with nine zoom-ins showing observations of the star on nine different days, and one summary zoom-in showing the path of the star relative to a background star over that span of time. The zoom-ins show the position and light pattern of the star LAWD 37 changing over time. The color key shows which Hubble WFC3 filters were used to create the image and which color is assigned to each filter. Filter F555W is in blue and F814W is in orange. The scale bar is labeled 5 arcseconds, and is about the same as the diameter of the glow surrounding the bright star. The zoom-in boxes span about 1.5 times the length of the scale bar, or about 7.5 arcseconds. The compass arrows indicate the orientation of the image on the sky. The north arrow points straight up. The east arrow points straight left.

Compass Image for White Dwarf Star LAWD 37

This graphic shows how microlensing was used to measure the mass of a white dwarf star. The dwarf, called LAWD 37, is a burned-out star in the center of this Hubble Space Telescope image. Though its nuclear fusion furnace has shut down, trapped heat is sizzling on the surface at...

This animation shows the motion of a white dwarf star passing in front of a distant background star. During the passage, the faraway star appears to change its position slightly, because its light path has been deflected by the white dwarf's gravity. Employing this trick of nature astronomers using NASA's Hubble Space Telescope have for the first time directly measured the mass of a single, isolated white dwarf — the surviving core of a burned out Sun-like star.

Mass Determination of Single White Dwarf

This animation shows the motion of a white dwarf star passing in front of a distant background star. During the passage, the faraway star appears to change its position slightly, because its light path has been deflected by the white dwarf's gravity. Employing this trick of...

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Last Updated
Mar 28, 2025
Contact
Media

Claire Andreoli
NASA’s Goddard Space Flight Center
Greenbelt, Maryland
claire.andreoli@nasa.gov

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