Hubble astronomers have uncovered, for the first time, a population of infant stars in the Milky Way satellite galaxy, the Small Magellanic Cloud (SMC, visible to the naked eye in the southern constellation Tucana), located 210,000 light-years away.
Hubble's exquisite sharpness plucked out an underlying population of infant stars embedded in the nebula NGC 346 that are still forming from gravitationally collapsing gas clouds. They have not yet ignited their hydrogen fuel to sustain nuclear fusion. The smallest of these infant stars is only half the mass of our Sun.
Although star birth is common within the disk of our galaxy, this smaller companion galaxy is more primeval in that it lacks a large percentage of the heavier elements that are forged in successive generations of stars through nuclear fusion.
Fragmentary galaxies like the SMC are considered primitive building blocks of larger galaxies. Most of these types of galaxies existed far away, when the universe was much younger. The SMC offers a unique nearby laboratory for understanding how stars arose in the early universe. Nestled among other starburst regions with the small galaxy, the nebula NGC 346 alone contains more than 2,500 infant stars.
The Hubble images, taken with the Advanced Camera for Surveys, identify three stellar populations in the SMC and in the region of the NGC 346 nebula - a total of 70,000 stars. The oldest population is 4.5 billion years, roughly the age of our Sun. The younger population arose only 5 million years ago (about the time Earth's first hominids began to walk on two feet). Lower-mass stars take longer to ignite and become full-fledged stars, so the protostellar population is 5 million years old. Curiously, the infant stars are strung along two intersecting lanes in the nebula, resembling a "T" pattern in the Hubble plot.
The observations, by Antonella Nota of the European Space Agency (ESA) and the Space Telescope Science Institute (STScI), Baltimore, Md., are being presented today at the meeting of the American Astronomical Society in San Diego, Calif.
The other science team members are: M. Sirianni (STScI/ESA), E. Sabbi (Univ. of Bologna), M. Tosi (INAF - Bologna Observ.), J.S. Gallagher (Univ. of Wisconsin), M. Meixner (STScI), M. Clampin (GSFC), S. Oey (Univ. of Michigan), A. Pasquali (ETH Zurich), L. Smith (Univ. College London), and R. Walterbos (New Mexico State Univ.).
Credits
NASA, ESA and A. Nota (STScI/ESA)| About The Object | |
|---|---|
| Object Name | NGC 346 |
| Object Description | Cluster and Nebulosity in the Small Magellanic Cloud |
| R.A. Position | 00h 59m 17.99s |
| Dec. Position | -72° 10' 48.0" |
| Constellation | Tucana |
| Distance | 210,000 light-years away (64,000 parsecs) |
| Dimensions | This image is 4.7 arcminutes (280 light-years or 87 parsecs). |
| About The Data | |
| Data Description | The Hubble image was created from HST data from proposal : A. Nota (STScI/ESA), M. Sirianni (STScI/ESA), E. Sabbi (Univ. of Bologna), M. Tosi (INAF - Bologna Observ.), J.S. Gallagher (Univ. of Wisconsin), M. Meixner (STScI), M. Clampin (GSFC), S. Oey (Univ. of Michigan), A. Pasquali (ETH Zurich), L. Smith (Univ. College London), and R. Walterbos (New Mexico State Univ.). |
| Instrument | HST>ACS/WFC |
| Exposure Dates | July 2004 |
| Filters | F555W (V), F814W (I) |
| About The Image | |
| Color Info | Blue: F555W (V) Green: F555W (V) + 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. |
