April 13, 2024

The Hunt for Cosmic Dawn: HERA Doubles Sensitivity to Unlock the Secrets of the Early Universe

When the radio dishes are fully online and adjusted, preferably this fall, the team hopes to build a 3D map of the bubbles of ionized and neutral hydrogen as they developed from about 200 million years ago to around 1 billion years after the Big Bang. The map might tell us how early stars and galaxies differed from those we see around us today, and how deep space as a whole searched in its teenage years.
The Milky Way Galaxy in the nighttime sky above the HERA range. The telescope is only able to observe between April and September, when the Milky Way is below the horizon, because the galaxy produces a lot of radio noise that interferes with the detection of faint radiation from the Epoch of Reionization.
” This is moving towards a possibly innovative method in cosmology. When you can come down to the level of sensitivity you require, theres so much information in the information,” stated Joshua Dillon, a research scientist in the University of California, Berkeleys Department of Astronomy and lead author of the paper. “A 3D map of most of the luminous matter in deep space is the objective for the next 50 years or more.”
Other telescopes likewise are peering into the early universe. The brand-new James Webb Space Telescope (JWST) has now imaged a galaxy that existed about 325 million years after the birth of deep space in the Big Bang. The JWST can see only the brightest of the galaxies that formed throughout the Epoch of Reionization, not the smaller sized however far more numerous dwarf galaxies whose stars heated the intergalactic medium and ionized most of the hydrogen gas.
HERA looks for to find radiation from the neutral hydrogen that filled the space in between those early stars and galaxies and, in particular, determine when that hydrogen stopped soaking up or discharging radio waves due to the fact that it became ionized.
The truth that the HERA team has not yet spotted these bubbles of ionized hydrogen within the cold hydrogen of the cosmic dark age dismiss some theories of how stars developed in the early universe.
Particularly, the information reveal that the earliest stars, which might have formed around 200 million years after the Big Bang, included couple of other components than hydrogen and helium. This is different from the structure of todays stars, which have a variety of so-called metals, the astronomical term for aspects, ranging from lithium to uranium, that are heavier than helium. The finding is consistent with the present design for how stars and outstanding explosions produced the majority of the other aspects.
” Early galaxies have to have been significantly various than the galaxies that we observe today in order for us not to have seen a signal,” stated Aaron Parsons, principal private investigator for HERA and a UC Berkeley associate teacher of astronomy. “In specific, their X-ray attributes have to have actually altered. Otherwise, we would have detected the signal were trying to find.”
The atomic structure of stars in the early universe figured out for how long it required to warm the intergalactic medium as soon as stars began to form. Secret to this is the high-energy radiation, mostly X-rays, produced by binary stars where among them has collapsed into a great void or neutron star and is gradually eating its companion. With few heavy aspects, a great deal of the buddys mass is blown away rather of falling onto the great void, meaning fewer X-rays and less heating of the surrounding area.
The new information fit the most popular theories of how stars and galaxies initially formed after the Big Bang, but not others. Preliminary outcomes from the very first analysis of HERA data, reported a year earlier, hinted that those options– particularly, cold reionization– were not likely.
” Our outcomes need that even before reionization and by as late as 450 million years after the Big Bang, the gas in between galaxies must have been warmed by X-rays. These likely came from binary systems where one star is losing mass to a buddy great void,” Dillon said. “Our results show that if thats the case, those stars need to have been extremely low metallicity, that is, very few components aside from hydrogen and helium in contrast to our sun, which makes sense since were talking about a duration in time in deep space prior to the majority of the other aspects were formed.”
The Epoch of Reionization
The origin of the universe in the Big Bang 13.8 billion years earlier produced a hot cauldron of energy and primary particles that cooled for hundreds of thousands of years before electrons and protons combined to form atoms– primarily hydrogen and helium. Looking at the sky with sensitive telescopes, astronomers have actually mapped in information the faint variations in temperature from this minute– whats referred to as the cosmic microwave background– a simple 380,000 years after the Big Bang.
Aside from this relict heat radiation, nevertheless, the early universe was dark. As deep space expanded, the clumpiness of matter seeded stars and galaxies, which in turn produced radiation– ultraviolet and X-rays– that heated up the gas in between stars. At some point, hydrogen began to ionize– it lost its electron– and formed bubbles within the neutral hydrogen, marking the start of the Epoch of Reionization.
To map these bubbles, HERA and numerous other experiments are concentrated on a wavelength of light that neutral hydrogen gives off and soaks up, but ionized hydrogen does not. Called the 21-centimeter line (a frequency of 1,420 megahertz), it is produced by the hyperfine shift, during which the spins of the electron and proton flip from parallel to antiparallel. Ionized hydrogen, which has actually lost its only electron, doesnt take in or release this radio frequency.
Because the Epoch of Reionization, the 21-centimeter line has actually been red-shifted by the expansion of the universe to a wavelength 10 times as long– about 2 meters, or 6 feet. HERAs rather basic antennas, a construct of chicken wire, PVC pipeline, and telephone poles, are 14 meters across in order to gather and focus this radiation onto detectors.
” At two meters wavelength, a chicken wire mesh is a mirror,” Dillon said. “And all the sophisticated stuff, so to speak, remains in the supercomputer backend and all of the data analysis that comes after that.”
The brand-new analysis is based on 94 nights of observing in 2017 and 2018 with about 40 antennas– phase 1 of the selection. In 2015s initial analysis was based upon 18 nights of phase 1 observations.
The new papers main outcome is that the HERA group has actually enhanced the level of sensitivity of the selection by an element of 2.1 for light given off about 650 million years after the Big Bang (a redshift, or a boost in wavelength, of 7.9), and 2.6 for radiation emitted about 450 million years after the Big Bang (a redshift of 10.4).
The HERA team continues to improve the telescopes calibration and information analysis in hopes of seeing those bubbles in the early universe, which are about 1 millionth the intensity of the radio noise in the community of Earth. Filtering out the regional radio noise to see the radiation from the early universe has actually not been simple.
” If its Swiss cheese, the galaxies make the holes, and were looking for the cheese,” up until now, unsuccessfully, said David Deboer, a research study astronomer in UC Berkeleys Radio Astronomy Laboratory.
Extending that example, however, Dillon noted, “What weve done is weve said the cheese needs to be warmer than if nothing had taken place. If the cheese were truly cold, it ends up it would be easier to observe that patchiness than if the cheese were warm.”
That mostly eliminate cold reionization theory, which posited a cooler starting point. The HERA scientists presume, rather, that the X-rays from X-ray binary stars warmed up the intergalactic medium.
” The X-rays will effectively heat up the entire block of cheese prior to the holes will form,” Dillon stated. “And those holes are the ionized bits.”
” HERA is continuing to improve and set better and much better limitations,” Parsons stated. “The truth that were able to keep pressing through, and we have brand-new techniques that are continuing to flourish for our telescope, is fantastic.”
Reference: “Improved Constraints on the 21 cm EoR Power Spectrum and the X-Ray Heating of the IGM with HERA Phase I Observations” by The HERA Collaboration: Zara Abdurashidova, Tyrone Adams, James E. Aguirre, Paul Alexander, Zaki S. Ali, Rushelle Baartman, Yanga Balfour, Rennan Barkana, Adam P. Beardsley, Gianni Bernardi, Tashalee S. Billings, Judd D. Bowman, Richard F. Bradley, Daniela Breitman, Philip Bull, Jacob Burba, Steve Carey, Chris L. Carilli, Carina Cheng, Samir Choudhuri, David R. DeBoer, Eloy de Lera Acedo, Matt Dexter, Joshua S. Dillon, John Ely, Aaron Ewall-Wice, Nicolas Fagnoni, Anastasia Fialkov, Randall Fritz, Steven R. Furlanetto, Kingsley Gale-Sides, Hugh Garsden, Brian Glendenning, Adélie Gorce, Deepthi Gorthi, Bradley Greig, Jasper Grobbelaar, Ziyaad Halday, Bryna J. Hazelton, Stefan Heimersheim, Jacqueline N. Hewitt, Jack Hickish, Daniel C. Jacobs, Austin Julius, Nicholas S. Kern, Joshua Kerrigan, Piyanat Kittiwisit, Saul A. Kohn, Matthew Kolopanis, Adam Lanman, Paul La Plante, David Lewis, Adrian Liu, Anita Loots, Yin-Zhe Ma, David H.E. MacMahon, Lourence Malan, Keith Malgas, Cresshim Malgas, Matthys Maree, Bradley Marero, Zachary E. Martinot, Lisa McBride, Andrei Mesinger, Jordan Mirocha, Mathakane Molewa, Miguel F. Morales, Tshegofalang Mosiane, Julian B. Muñoz, Steven G. Murray, Vighnesh Nagpal, Abraham R. Neben, Bojan Nikolic, Chuneeta D. Nunhokee, Hans Nuwegeld, Aaron R. Parsons, Robert Pascua, Nipanjana Patra, Samantha Pieterse, Yuxiang Qin, Nima Razavi-Ghods, James Robnett, Kathryn Rosie, Mario G. Santos, Peter Sims, Saurabh Singh, Craig Smith, Hilton Swarts, Jianrong Tan, Nithyanandan Thyagarajan, Michael J. Wilensky, Peter K. G. Williams, Pieter van Wyngaarden and Haoxuan Zheng, 19 January 2023, The Astrophysical Journal.DOI: 10.48550/ arXiv.2210.04912.
The HERA partnership is led by UC Berkeley and includes researchers from across North America, Europe and South Africa. The construction of the selection is moneyed by the National Science Foundation and the Gordon and Betty Moore Foundation, with crucial support from the federal government of South Africa and the South African Radio Astronomy Observatory (SARAO).

The JWST can see just the brightest of the galaxies that formed during the Epoch of Reionization, not the smaller however far more various dwarf galaxies whose stars heated up the intergalactic medium and ionized many of the hydrogen gas.
The atomic composition of stars in the early universe identified how long it took to heat up the intergalactic medium when stars started to form. Key to this is the high-energy radiation, mainly X-rays, produced by binary stars where one of them has actually collapsed into a black hole or neutron star and is slowly eating its companion. “Our outcomes show that if thats the case, those stars need to have been extremely low metallicity, that is, really couple of elements other than hydrogen and helium in contrast to our sun, which makes sense because were talking about a period in time in the universe before many of the other components were formed.”
As the universe broadened, the clumpiness of matter seeded stars and galaxies, which in turn produced radiation– ultraviolet and X-rays– that warmed the gas between stars.

The Hydrogen Epoch of Reionization Array (HERA) includes 350 dishes pointed upward to spot 21-centimeter emissions from the early universe. It lies in a radio-quiet region of the dry Karoo in South Africa. Credit: Dara Storer
The newest information from HERA enhances the look for cosmic dawn radiation and tests theories of galaxy development.
A range of 350 radio telescopes situated in the Karoo desert of South Africa is getting closer to identifying “cosmic dawn”– the time duration following the Big Bang when stars initially ignited and galaxies formed.
The Hydrogen Epoch of Reionization Array (HERA) group has revealed in a paper accepted for publication in The Astrophysical Journal that they have doubled the sensitivity of the range, which was currently the most delicate radio telescope in the world dedicated to exploring this special duration in the history of the universe.
While they have yet to actually spot radio emissions from the end of the cosmic dark ages, their outcomes do provide clues to the structure of stars and galaxies in the early universe. In particular, their information recommend that early galaxies included extremely few components besides hydrogen and helium, unlike our galaxies today.