Astronomers from MIT and Arizona State University report that a table-sized radio antenna in a remote region of western Australia has picked up faint signals caused by the very first stars that formed in the universe, some 180 million years after the Big Bang.
“This is the first real signal that stars are starting to form, and starting to affect the medium around them,” says study co-author Alan Rogers, a scientist at MIT’s Haystack Observatory. “What’s happening in this period is that some of the (UV) radiation from the very first stars is starting to allow hydrogen to be seen. It’s causing hydrogen to start absorbing the background radiation, so you start seeing it in silhouette, at particular radio frequencies.”
The results of this study have been published in Nature by ASU School of Earth and Space Exploration astronomer Judd Bowman, with co-authors Alan Rogers of the Massachusetts Institute of Technology's Haystack Observatory, Raul Monsalve of the University of Colorado, and Thomas Mozdzen and Nivedita Mahesh also of ASU's School of Earth and Space Exploration.
Here is a brilliant explanation of the discovery by NSF's Peter Kurczynski -
Formation of the First Stars
About 400 thousand years after the the Big Bang, the universe was filled with hot plasma. There were no stars or galaxies, and the universe was filled primarily with neutral hydrogen gas.
In the next 50-100 million years, the early universe was expanding, but the densest regions of the universe were collapsing under gravity to form the first stars.
What happened next is described by Karl Glazebrook, Director & Distinguished Professor, Centre for Astrophysics & Supercomputing, Swinburne University of Technology -
The formation of the first stars had a dramatic effect on the rest of the universe. Ultraviolet radiation from them changed the electron spin in the hydrogen atoms, causing it to absorb the background radio emission of the universe at a natural resonant frequency of 1,420 MHz, casting a shadow so to speak.
Now, 13 billion years later, that shadow would be expected at a much lower frequency because the universe has expanded nearly 18-fold in that time.
Detecting the Signature of the Early Stars
Scientists have been searching for this extremely faint shadow of a signal for years in the 0-200 MHz spectrum. Now, after 12 years of experimental effort, using the EDGES radio wave detector located in western Australia, Bowman and his team have detected the signal — a dip in the strength of radio waves around the 78 MHz region. It took over two years to verify and validate the measurements and reach the conclusion that the signals represent the absorption of the cosmic background radiation.
Dark Matter and Dark Energy
The study also revealed a surprise — the dip of the signal level is deeper than expected. Implying that gas in the early universe was probably much colder than expected (less than half the expected temperature), thus absorbing more of the background light.
The authors explain -
Of the proposed extensions to the standard model of cosmology and particle physics, only cooling of the gas as a result of interactions between dark matter and baryons seems to explain the observed amplitude.
Work done by theoretical astrophysicist Rennan Barkana of Tel Aviv University in Israel (with whom Judd Bowman shared the odd findings) has suggested hydrogen gas could be cooled by interactions with dark matter particles that are relatively light (estimated mass of a few protons), as opposed to the heavier mass people have been theorizing. Prof. Barkana published a companion paper in the same issue of Nature.
If this is truly caused by interaction between ordinary matter and dark matter, then this would be the first time scientists have observed an effect of dark matter other than its gravitational force.
Theoretical astrophysicist Katie Mack writes -
If this signal really is detecting a new kind of dark matter interaction, it’s not only the first confirmation of dark matter making its presence felt, it’s also a magnificent confirmation that dark matter is a real, tangible component of the cosmos. In short, if this signal is what it looks like, it changes everything.
The EDGES Radio Spectrometer
The Experiment to Detect the Global EoR Signature (EDGES) is a collaboration between ASU and MIT, with funding from the U.S. NSF and site support from the Australian CSIRO. EDGES is located at the Murchison Radio-astronomy Observatory (MRO) in Western Australia.
This location was chosen due to its radio-quiet conditions below 200 MHz. Many FM radio stations use this spectrum. The initial radio-quiet zone was a protected zone in a 70 km radius around the MRO, in which all radio apparatus licenses needed to be made with the approval of the MRO governing body. The enhanced radio-quiet zone adds a second zone, effectively extending the license approval governing area from a radius of 70 km to 150 km.
Radio waves are collected by the antenna consisting of two rectangular metal panels mounted horizontally on fiberglass legs above a metal mesh. Signals are analyzed using a digital radio spectrometer located in a hut 100 meters away. You can learn about the project and the antenna at loco.lab.asu.edu/...
The Square Kilometre Array (SKA)
Barkana predicts that the dark matter produced a specific pattern of radio waves that can be detected with a large array of radio antennas. One such array is the Square Kilometre Array (SKA).
The Square Kilometre Array (SKA) project is an international effort to build the world’s largest radio telescope, with eventually over a square kilometre (one million square metres) of collecting area. Hundreds and eventually thousands of mid to high frequency 15m dishes will be located in South Africa and Africa and hundreds of thousands and eventually up to a million low-frequency antennas will be located in Western Australia.
Next Steps
“It is unlikely that we’ll be able to see any earlier into the history of stars in our lifetimes,” lead author Bowman of ASU says. “This project shows that a promising new technique can work and has paved the way for decades of new astrophysical discoveries.”
The next steps are for other instruments and researchers to confirm this team's detection and to keep improving the accuracy of the instruments. And keep looking for answers to questions such as —
- What was present at the moment of the Big Bang? Nothing? No space, no time?
- What happened before the Big Bang? Is that a nonsensical question?
- If space is expanding, what is it expanding into?
- Is space finite? Yes. Is time finite?
- What is dark matter? Why is there so much of it even though we cannot detect it?
- Does Physics predict sentient beings created from the Big Bang plasma, who billions of years later peer back in time to study the origins of the Universe?
- Are we alone?
References
- Bowman et al, An absorption profile centred at 78 megahertz in the sky-averaged spectrum - www.nature.com/…
- Rennan Barkana, Possible interaction between baryons and dark-matter particles revealed by the first stars — www.nature.com/...
- Katie Mack, A Potentially Game-Changing Message from the Dawn of Time — blogs.scientificamerican.com/…
- Karl Glazebrook, Signal detected from the first stars in the universe, with a hint that dark matter was involved — theconversation.com/…
- Astronomers detect earliest evidence yet of hydrogen in the universe — news.mit.edu/…
- Sean Carroll, Dark Matter and the Earliest Stars — www.preposterousuniverse.com/...
- Experiment to Detect the Global EoR Signature (EDGES) — loco.lab.asu.edu/...