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 180,000 degrees Fahrenheit, causing the stellar remnant to glow fiercely.
The inset boxes at right plot how the dwarf passed in front of a background star in 2019. The wavy blue line traces the dwarf's apparent motion across the sky as seen from Earth. Though the dwarf is following a straight trajectory, the motion of Earth orbiting the Sun imparts an apparent sinusoidal offset due to parallax. (The star is only 15 light-years away, and therefore is moving at a faster rate against the stellar background.)
As it passed by the fainter background star, the dwarf's gravitational field warped space (as Einstein's theory of general relativity predicted a century ago). And this deflection was precisely measured by Hubble's extraordinary resolution. The dwarf's offset position is colored orange.
The amount of deflection yields a mass for the white dwarf of 56 percent our Sun's mass, and this provides insights into theories of the structure and composition of white dwarfs. This is the first time that astronomers directly measured the mass of a single, isolated white dwarf star, thanks to a "funhouse mirror" trick of nature.
The white dwarf has a "spike" because it is so bright the light "bled" into the Hubble camera's CCD detector. This interfered with one of the observing dates for measuring that background star's position on the sky.
The compass graphic points to the object's orientation on the celestial sphere. North points to the north celestial pole which is not a fixed point in the sky, but it currently lies near the star, Polaris, in the circumpolar constellation Ursa Minor. Celestial coordinates are analogous to a terrestrial map, though east and west are transposed because we are looking up rather than down.
Credits
Science
NASA, ESA, Peter McGill (UC Santa Cruz, IoA), Kailash Sahu (STScI)
Image Processing
Joseph DePasquale (STScI)
| About The Object | |
|---|---|
| Object Name | LAWD 37 (LP 145-141) |
| Object Description | Isolated White Dwarf |
| R.A. Position | 11:45:42.9205 |
| Dec. Position | -64:50:29.459 |
| Constellation | Musca |
| Distance | About 15 light-years |
| Dimensions | Image is 1.2 arcmin across (about 0.005 light-years) |
| About The Data | |
| Data Description | This image was created with Hubble data from proposals: 15705 , 15961 , and 16251 (K. Sahu). |
| Instrument | WFC3/UVIS |
| Exposure Dates | 9 pointings between May 2019 and Sep 2020 |
| Filters | F555W, F814W |
| About The Image | |
| Color Info | These images are a composite of separate exposures acquired by the Hubble Space Telescope using the WFC3/UVIS instrument. Several filters were used to sample specific wavelength ranges. The color results from assigning different hues (colors) to each monochromatic (grayscale) image associated with an individual filter. In this case, the assigned colors are: Cyan: F555W, Orange: F814W |
| About The Object | |
|---|---|
| Object Name | A name or catalog number that astronomers use to identify an astronomical object. |
| Object Description | The type of astronomical object. |
| R.A. Position | Right ascension – analogous to longitude – is one component of an object's position. |
| Dec. Position | Declination – analogous to latitude – is one component of an object's position. |
| Constellation | One of 88 recognized regions of the celestial sphere in which the object appears. |
| Distance | The 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. |
| Dimensions | The physical size of the object or the apparent angle it subtends on the sky. |
| About The Data | |
| Data Description |
|
| Instrument | The science instrument used to produce the data. |
| Exposure Dates | The date(s) that the telescope made its observations and the total exposure time. |
| Filters | The camera filters that were used in the science observations. |
| About The Image | |
| Image Credit | The primary individuals and institutions responsible for the content. |
| Publication Date | The date and time the release content became public. |
| Color Info | A brief description of the methods used to convert telescope data into the color image being presented. |
| Orientation | The rotation of the image on the sky with respect to the north pole of the celestial sphere. |
