The Least Luminous Known Galaxy

The Least Luminous Known Galaxy

Astronomers’ observations of the universe1 provide substantial support for the cosmic creation event taught in the Bible.2 Evidence shows that the universe is comprised predominantly of dark energy (energy embedded in the space surface of the universe that causes the cosmic surface to expand faster and faster as the universe ages) and cold exotic dark matter (slow moving particles that weakly interact with photons). However, this cosmic model predicts that thousands of cold exotic dark matter haloes should accompany large galaxies. Astronomers should detect populations of dwarf galaxies filled with stars produced by the ordinary matter (protons, neutrons, and electrons) attracted to the haloes through their gravitational pull.

Astronomers don’t see nearly enough of these galaxies to satisfy the prediction arising from the dark-energy dominated, cold-exotic-dark-matter (ΛCDM) model. The model predicts more than ten times as many exotic dark matter haloes than the number of dwarf galaxies astronomers have actually detected. This shortfall is known as the “missing galaxies” problem.

The problem once was much worse. Just three years ago astronomers acknowledged a shortfall of more than a factor of a hundred in the number of dwarf galaxies associated with large galaxies. However, in recent years researchers have discovered a number of super-faint dwarf galaxies in the vicinity of the Milky Way Galaxy (MWG), the Andromeda Galaxy, and other large nearby galaxies. Astronomers now recognize that the missing dwarf galaxies problem is at least partly solved by understanding that these galaxies are more difficult to detect than originally thought.

Now, a team of seven American astronomers has found a dwarf galaxy so extremely dim in its light output that if it were to prove typical of dwarf galaxies in general, there would be no missing galaxies problem.3 The galaxy is called Segue 1. It is practically inside our MWG. It spatially overlaps the leading arm of the Sagittarius stream. Because of the proximity of Segue 1, astronomers were able to detect it with their largest telescopes.

Segue 1 is so faint that its combined light output has an absolute magnitude measure of only -1.5. In astronomy, the smaller the absolute magnitude of an object is, the brighter the object. The Sun’s absolute magnitude is +4.8. Rigel, the second brightest star in the constellation of Orion, has an absolute magnitude of -8.1. Each unit of magnitude is equivalent to a factor of 2.512 in brightness. Therefore, Rigel has about 158,000 times the light output of the Sun and Rigel is more than four hundred times brighter than Segue 1!

In their research paper the American team presented spectroscopic evidence proving that Segue 1 is dominated by dark matter, most likely exotic dark matter. Such dominance explains why Segue 1 manifests such a low luminosity.

The proximity of Segue 1, plus its domination by dark matter, makes it the best-known candidate for detecting gamma rays from the annihilation of exotic dark matter particles. Such a discovery could help silence the critics of big bang cosmology, such as young-earth creationists, who claim that exotic dark matter is a myth. It also would give astronomers useful insight into the nature of the exotic matter.

Segue 1 represents one more example of the principle that the more astronomers learn about the universe, the more evidence they uncover in support of the biblical cosmic creation model–and its Creator.

  1. Hugh Ross, The Creator and the Cosmos, 3rd ed. (Colorado Springs: NavPress, 2001), 23-29.
  2. Ibid., 31-67, 99-199; Hugh Ross, Why the Universe Is the Way It Is (Grand Rapids: Baker, 2008), 27-106, 209-14
  3. Marla Geha et al., “The Least-Luminous Galaxy: Spectroscopy of the Milky Way Satellite Segue 1,” Astrophysical Journal 692 (February 20, 2009): 1464-75.