Astronomers used the Hubble Space Telescope to unmask the dim, star-starved dwarf galaxy Leo IV. These Hubble images demonstrate why astronomers had a tough time spotting this small-fry galaxy.
The image at left shows part of the galaxy, outlined by the white rectangular box. The box measures 83 light-years wide by 163 light-years long. The few stars in Leo IV are lost amid neighboring stars and distant galaxies.
A close-up view of the background galaxies within the box is shown in the middle image. The image at right shows only the stars in Leo IV. The galaxy, which contains several thousand stars, is composed of Sun-like stars, fainter, red dwarf stars, and some red giant stars brighter than the Sun. Astronomers discovered Leo IV in Sloan Digital Sky Survey images by spotting a region where a clump of stars was huddled closer together than stars in areas around it.
Residing 500,000 light-years from Earth, Leo IV is one of more than a dozen ultra-faint dwarf galaxies found lurking around our Milky Way galaxy. These galaxies are dominated by dark matter, an invisible substance that makes up the bulk of the universe's mass.
Astronomers used Hubble to measure the ages of the stars in Leo IV and two other ultra-faint dwarf galaxies. The measurements revealed that the stars in all three galaxies are more than 13 billion years old, almost as old as the 13.7-billion-year-old universe. Because the stars in these galaxies are so ancient and share the same age, astronomers suggest that a global event, such as reionization, shut down star formation in them. Reionization is a transitional phase in the early universe when the first stars burned off a fog of cold hydrogen.
The Hubble image is a composite of exposures taken in January 2012 by the Advanced Camera for Surveys.
Credits
NASA, ESA, and T. Brown (STScI)| About The Object | |
|---|---|
| Object Name | Leo IV |
| Object Description | Ultra-Faint Dwarf Galaxy |
| R.A. Position | 11h 32m 56.99s |
| Dec. Position | 00° 31' 59.98" |
| Constellation | Leo |
| Distance | 500,000 light-years (150,000 parsecs) |
| About The Data | |
| Data Description | The image was created from Hubble data from proposal : T. Brown (STScI), et al. The science team comprises T. Brown and J. Tumlinson (STScI), M. Geha (Yale University), E. Kirby (California Institute of Technology), D. VandenBerg (University of Victoria), R. Munoz (Universidad de Chile), J. Kalirai (STScI), J. Simon (Observatories of the Carnegie Institute of Washington), R. Avila (STScI), P. Guhathakurta (UCO/Lick Observatory), A. Renzini (Osservatorio Astronomico), and H. Ferguson (STScI). |
| Instrument | HST>ACS/WFC |
| Exposure Dates | January 1, 2012, Exposure Time: 11.4 hours |
| Filters | F606W (V) and F814W (I) |
| About The Image | |
| Color Info | This image is a composite of separate exposures acquired by the ACS instrument. Several filters were used to sample various wavelengths. 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: Blue: F606W (V) Orange: 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. |
