Peering deep into the star-filled, ancient hub of our Milky Way (left), the Hubble Space Telescope has found a rare class of oddball stars called blue stragglers, the first time such objects have been detected within our galaxy's bulge.
Blue stragglers – so named because they seem to be lagging behind in their rate of aging compared with the population from which they formed – were first found inside ancient globular star clusters half a century ago.
This discovery is a spin-off from a seven-day-long survey conducted in 2006 called the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS). Hubble peered at and obtained variability information for 180,000 stars in the crowded central bulge of our galaxy, 26,000 light-years away. The picture at right shows the 42 blue straggler candidates circled in green.
Blue stragglers have long been suspected to be located in the bulge. Until now, it has never been proven because younger stars in the disk of our galaxy lie along the line-of-sight to the core, confusing and contaminating the view. But Hubble's view is so sharp that astronomers could distinguish the motion of the core population from foreground stars in the Milky Way.
It's not clear how blue stragglers form, or if there is more than one mechanism at work. A common idea is that two stars collide and merge. This stirs up hydrogen fuel and causes the resulting, more massive star to undergo nuclear fusion at a faster rate, causing it to burn hotter and bluer.
The visible-light observations were made with Hubble's Advanced Camera for Surveys.
Credits
NASA, ESA, W. Clarkson (Indiana University and UCLA), and K. Sahu (STScI);Acknowledgment: A. Fujii
| About The Object | |
|---|---|
| Object Name | SWEEPS Field |
| Object Description | Milky Way Galactic Bulge (left), and Stellar Field Near the Galactic Bulge (inset) |
| R.A. Position | 17h 58m 59.99s |
| Dec. Position | -29° 12' 0.0" |
| Constellation | Sagittarius |
| About The Data | |
| Data Description | This image (inset) was created from HST data from proposal : K. Sahu, R. Gilliland, H. Bond, S. Casertano, M. Livio, and N. Panagia (STScI), T. Brown (University Corporation for Atmospheric Research), D. Minniti (Catholic University of Chile), A. Renzini (Astronomical Observatory of Padova, Italy), R. Rich (University of California, Los Angeles), and M. Zoccali (Catholic University of Chile). The science findings also include data taken with the HST proposal : K. Sahu (STScI) et al. Additional members of the science team include W. Clarkson (Indiana University and UCLA), and T. Brown, E. Smith, and J. Anderson (STScI). |
| Instrument | HST>ACS/WFC |
| Exposure Dates | February 22 - 29, 2004, Exposure Time: 49 hours |
| Filters | F606W (R) and F814W (I) |
| About The Image | |
| Color Info | This image (inset) is a composite of many separate exposures made by the ACS instrument on the Hubble Space Telescope using two different filters. Two filters were used to sample broad wavelength ranges. The color results from assigning different hues (colors) to each monochromatic image. In this case, the assigned colors are: Blue: F606W (R) Green: F606W (R) + F814W (I) Red: F814W (I) |
| Compass Image |  |
| 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. |
