“Very soon the heavens presented an extraordinary appearance, for all the stars directly behind me were now deep red, while those directly ahead were violet,” is how philosopher and science-fiction author Olaf Stapledon described the phenomena known as “redshift” in his science fiction novel, Star Maker, a history of life in the universe. In 1929, Edwin Hubble discovered that the universe is expanding, with most other galaxies moving away from us. Light from these galaxies is shifted to longer (further away and redder) wavelengths – in other words, it is red-shifted, a result of the expansion of the universe.
Quasar –Bright as 600 Trillion Suns
A single quasar can outshine 10,000 galaxies for millions of years. In January 2019, astronomers using data from the Nasa/ESA Hubble Space Telescope announced that the discovery of the brightest quasar ever seen in the early universe with a brightness of about 600 trillion suns –by far the brightest nucleus ever found of an active galaxy and its powerful glow created by the energy released by gas falling towards the supermassive black hole at its center several hundred million times as massive as our sun. Ancient quasars can provide an insight into the birth of galaxies when the universe was about one billion years old.
The “Redshift” Galaxy
Fast forward to this week, astronomers at the Instituto de Astrofisica de Canarias (IAC) have announced the discovery of a galaxy with a ultraviolet luminosity comparable to that of a quasar using observations made with the Gran Telescopio Canarias (GTC), at the Roque de los Muchachos Observatory in the Canary Islands, and with the ATACAMA Large Millimetre/submillimetre Array (ALMA), in Chile.
The galaxy, called BOSS-EUVLG1, has a red-shift of 2.47. This is a measure of the reddening of the light coming from the galaxy, and can be used to find its distance, the further away the galaxy, the greater the value. For BOSS-EUVLG1, the value of 2.47 means that we are observing the galaxy when the universe was some 2 thousand million years old, around 20% of its present age.
In the image above, left and center: shows the region of the sky containing BOSS-EUVLG1, which stands out due to its blue color. Credit: DESI Legacy Imaging Surveys. Right: Artist`s drawing of the burst of star formation in BOSS-EUVLG1, which contains a large number of young massive stars, and hardly any dust. (Gabriel Pérez Díaz, SMM, IAC).
The large values of redshift and luminosity of BOSS-EUVLG1 caused it to be classified previously in the BOSS (Baryon Oscillation Spectroscopic Survey) project as a quasar. However, from the observations made with the OSIRIS and EMIR instruments on the GTC, and with the millimetre wave telescope ALMA, the researchers have shown that it is not a quasar but in fact a galaxy with extreme, exceptional properties.
Young, Massive Stars –1000 Times Milky Way
The study revealed that the high luminosity of BOSS-EUVLG1 in the ultraviolet and in Lyman-alpha emission is due to the large number of young, massive stars in the galaxy. This high luminosity, well above the range for other galaxies, gave rise to its initial identification as a quasar. However, in quasars the high luminosity is due to the activity around the supermassive black holes in their nuclei, and not to star formation.
“BOSS-EUVLG1 seems to be dominated by a burst of formation of young, very massive stars, with hardly any dust, and with a very low metallicity, explains Rui Marques Chaves, a researcher at the CAB, formerly a doctoral student at the Instituto de Astrofísica de Canarias and the University of La Laguna (ULL), and first author of the article.
The rate of star formation in this galaxy is very high, around a thousand solar masses per year, around a thousand times higher than that in the Milky Way, although the galaxy is 30 times smaller. “This rate of star formation is comparable only to the most luminous infrared galaxies known, but the absence of dust in BOSS-EUVLG1 allows its ultraviolet and visible emission to reach us with hardly any attenuation”, explains Ismael Pérez Fournon, an IAC researcher and a co-author.
Brief Lifespan of High Luminosity in UV
So, the results of the study suggest that BOSS-EUVLG1 is an example of the initial phases of the formation of massive galaxies. In spite of its high luminosity and star formation rate, its low metallicity shows that the galaxy has hardly had time to enrich its interstellar medium with dust and newly formed metals. Nevertheless, “the galaxy will evolve towards a dustier phase, similar to the infrared galaxies, -notes Camilo E. Jiménez Ángel, a doctoral student at the IAC, and a co-author of the article-. Also, its high luminosity in the UV will last only a few hundred million years, a very short period in the evolution of a galaxy”.
“This would explain why other galaxies similar to BOSS-EUVLG1 have not been discovered”, observed Claudio Dalla Vecchia, a researcher at the IAC, and a co-author.
Image at the top of the page shows four ‘Ultra-Red’ galaxies that formed when our Universe was about a billion years old detected by a team of astronomers, led by Jiasheng Huang (Harvard-Smithsonian Center for Astrophysics) using the Spitzer Space Telescope.