BX442

Coordinates: 23^h 46^m 19.35^s, +12° 48′ 00.0″

BX442 (Q2343-BX442) is a grand design spiral galaxy of type Sc. It has a companion dwarf galaxy. It is the most distant known grand design spiral galaxy in the universe, with a redshift of z=2.1765 ± 0.0001. Although commonly referred to as the oldest known grand design spiral galaxy in the universe, it is more accurately the earliest such galaxy known to exist in the universe, with a lookback time (the difference between the age of the universe now and the age of the universe at the time light left the galaxy) of 10.7 billion years in the concordance cosmology. This time estimate means that structure seen in BX442 developed roughly 3 billion years after the Big Bang, 10 kiloparsecs (30,000 ly) in diameter, and has a mass of 6 × 10¹⁰solar masses.

The spiral morphology of BX442, while similar to many modern-day galaxies, makes it unusual in the young universe. According to study co-author Alice E. Shapley of UCLA: The vast majority of old galaxies look like train wrecks. Our first thought was, why is this one so different, and so beautiful?

The unusual spiral morphology of BX442 was discovered using images obtained from the Hubble Space Telescope by a team of astronomers led by David R. Law of the University of Toronto. While the Hubble image suggested the galaxy's spiral structure however, it didn't conclusively prove that the galaxy rotated like modern-day spiral galaxies. The team therefore used an integral-field spectrograph called OSIRIS (OH-Suppressing Infrared Imaging Spectrograph) at the W.M. Keck Observatory in Hawaii to confirm their discovery. In combination with a laser-guide-star adaptive optics system which corrects for distortions of incoming light caused by the Earth's turbulent atmosphere, the astronomers were able to sample the light from different parts of the galaxy. Small Doppler shifts of the light between different samples showed that BX442 was indeed a spiral disk, rotating roughly as fast as the Milky Way Galaxy, but much thicker and forming stars more rapidly.