- Who
- HD1
- What
- 13,500,000,000 year(s)
- Where
- Not Applicable ()
- When
The oldest known galaxy is HD1, a 13.5 billion-year-old galaxy which is located some 33.4 billion light-years away from Earth (redshift of 13.27). It was discovered as part of an international research project that involved 1,200 hours of observations using the Spitzer Space Telescope as well as the Subaru, UK Infrared and VISTA ground-based telescopes. The research was published in The Astrophysical Journal on 7 April 2022.
Astronomers are intrigued by the galaxy's extreme luminosity in ultraviolet wavelengths. Generally, strong ultraviolet light is evidence of a high rate of star formation, but HD1's brightness is so extreme that this explanation doesn't really make sense.
In the discovery paper, the team put forward two possible theories for the luminosity of the galaxy. The first is that the galaxy, which dates to the first few hundred million years after the Big Bang, is producing a large number of what are called "Population III" stars – a currently only hypothetical class of stars that formed from the primordial gas of the early universe. These stars were larger and brighter than later generations of stars.
The second possibility is that HD1 may have a supermassive black hole at its centre. If this proves correct, this would be the new oldest and most distant example, beating the previous record holder by more than 500 million years.
In order to answer these questions, HD1 has been added to the list of early observation priorities for the James Webb Space Telescope, whose 6.5-m aperture and infrared optics make it ideally suited to examine these primordial galaxies.
