Monday, May 2, 2022

Is This The Most Distant Galaxy - Or Is The Freakish (Z-Shift) Object HD1 Something Else?


                    Three -color image of HD 1 based on data from recent Ap J paper

Using the Atacama Large Millimeter/submillimeter Array, or ALMA — a collection of radio telescopes in Chile — a team of cosmologists lead by Yuichi Harikane and his team may have found the most distant galaxy yet, as reported in a recent issue of The Astrophysical Journal  (Vol.929, No. 1) :

A Search for H-Dropout Lyman Break Galaxies at z ∼ 12–16 (

 In particular they got a tentative redshift for HD1 of 13, meaning that the wavelength of the light emitted by an oxygen atom had been stretched to 14 times its wavelength at rest. Try to process that!  The other distant blob, HD2 is also under study but its redshift has not yet been determined.   But the data for the presumed galaxy HD1 tracks its existence to only 330 million years after the Big Bang, or smack in the hunting ground of the Webb telescope, which will also be able to confirm the redshift.

 That astronomic epoch of time is so far unexplored given it is so close to what we call the "decoupling" of matter from radiation.  The period is defined for when different types of particles fell out of thermal equilibrium with each other.   The effect basically being to make the mean free paths for particles (namely electrons) longer and hence the interaction rates less, meaning objects are more transparent to radiation.

This occurs as a result of the expansion of the universeIn the expanding universe, the farther an object is from us, the faster it is moving away, which motion causes an object’s light to shift to longer redder wavelengths.  This is based on applying the principle of the Doppler effect.   This is analogous to the sound of a receding ambulance siren shifting to a lower tone or frequency as it gets further away. The gold standard of cosmic distances, however is the redshift, derived by obtaining a spectrum of the object and measuring how much the wavelengths emitted by characteristic elements have increased or shifted to the red.  See e.g.

In search of the most distant galaxies the ALMA team sifted through some 70,000 objects, and HD1 was the reddest one they could find. It’s thought that HD1 may be home to the Universe’s very first stars, known as Population III stars, which until now have never been observed. In the words of the research paper's lead author, Yuichi Harikane:

HD1’s red color matched the expected characteristics of a galaxy 13.5 billion light years away surprisingly well, giving me a little bit of goose bumps when I found it,

Though the going bet is that the pair of HD objects are galaxies, the ALMA team can only guess for the time being. They may also be quasars or maybe something else entirely. What, exactly? Who knows? There can be no certainty until they get the chance to observe the objects directly with the new James Webb Space Telescope. But whatever they are, astronomers say, they could shed light on a crucial phase in the cosmos as it evolved from pristine primordial fire into planets, life and us. In the words of another co-author Fabio Pacucci of the Harvard-Smithsonian Center for Astrophysics:

I am excited as a kid who spots the very first firework in a magnificent and highly anticipated show. This could well be one of the first glimmers of light to illuminate the cosmos in a show that ultimately created every star, planet and even flower that we see around us today — more than 13 billion years later.”

Pacucci was part of the ALMA team led by Yuichi Harikane of the University of Tokyo that spent 1,200 hours using various ground-based telescopes to search for very early galaxies.    The  ALMA team basic observations of HD2 conforms more or less with those of HD1, but the other blob’s redshift has not been determined.  In the words of Marcia Rieke of the University of Arizona, who is a principal investigator for the Webb telescope:

If the redshift from ALMA can be confirmed, then this would indeed be a spectacular object,” 

According to the cosmological narrative thus far, the road to the material universe as we know it started about 100 million years after the Big Bang, when hydrogen and helium created in the primordial explosion began to condense into the first stars, known as Population III stars (Population I and II stars have large amounts of heavier elements, are present in galaxies today). Pop III stars, composed of only hydrogen and helium, have never been observed, and they would have been much bigger and brighter than the ones in the universe today. They would have burned hot and died fast in supernova explosions that then jump-started the chemical evolution polluting a pristine universe with elements like oxygen and iron, the stuff of us.

Pacucci said the ALMA team  first thought that HD1 and HD2 were what are called starburst galaxies, which billow with new stars. But after further research, they discovered that HD1 seemed to be producing stars more than 10 times faster than such galaxies usually do.

Another possibility, Pacucci said, is that this galaxy was birthing those very first ultra-luminous Population III stars. Yet another explanation is that all this radiance comes from material splashing into a supermassive black hole 100 million times the mass of the sun. But astronomers have trouble explaining how a black hole could have grown so big so early in cosmic time.  Avi Loeb, a co-author on Pacucci’s paper, and most famous for his paper on the strange object called Oumuamua, e.g.

1810.11490.pdf (

said in an interview:

HD1 would represent a giant baby in the delivery room of the early universe,” 

Giant baby or not, those of us invested in astronomy and cosmology can't wait to see what the Webb Telescope will reveal about these objects.

See Also:

 Meet HD1, The New Most Distant Galaxy Found 13.5 Billion Years Back In Time And Close To The ‘Big Bang’ (


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