How do astronomers weigh a star? These images help tell the story.
In the image at top, left, astronomers discovered a subtle brightening of a star [located within the box] due to the effect of gravitational microlensing. This phenomenon occurs when a foreground star, in this case a dim red star, passes in front of a much more distant star and amplifies its light. Astronomers were engaged in a large-scale search for microlensing events in the halo of our Milky Way galaxy. They were looking in the direction of the Large Magellanic Cloud, a satellite galaxy of our Milky Way. The image was taken in February 1993 with the 50-inch telescope at the Mount Stromlo Observatory in Australia. The box represents the field of view of NASA's Hubble Space Telescope.
When astronomers used the Mount Stromlo telescope to observe the same region almost a year later, the background star had returned to its normal brightness. The foreground star - the "natural lens" that had magnified the background star - had moved away. The ground-based telescope's vision, however, was not keen enough to resolve the stars separately.
So, astronomers used the sharp vision of the Hubble telescope to resolve the stars as two separate objects. The foreground star is red, and is in our galaxy's halo. The background star is blue, and is in the Large Magellanic Cloud. The image was taken on July 11, 2002.
Seeing the two stars allowed astronomers to calculate the foreground star's distance from Earth, which is 1,800 light-years. They already knew that the background star is 170,000 light-years away, the distance to the Large Magellanic Cloud. Knowing the distances to both stars then allowed astronomers to calculate the foreground star's mass, which is one-tenth the mass of the Sun.
Credits
NASA, ESA and D. Bennett (University of Notre Dame)| About The Object | |
|---|---|
| Object Name | MACHO-LMC-5, STAR-0516-7029 |
| Object Description | Stellar Binary System/Microlensing Object |
| R.A. Position | 05h 16m 40.99s |
| Dec. Position | -70° 29' 17.99" |
| Constellation | Dorado |
| About The Data | |
| Data Description | February 1993 (top left), January 1994 (bottom left), and July 11, 2002 (right) |
| Instrument | Mount Stromlo Observatory (left), and HST>ACS/WFC (right) |
| Exposure Dates | February 1993 (top left), January 1994 (bottom left), and July 11, 2002 (right) |
| 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. |
