Astronomy:Experiment to Detect the Global EoR Signature
The Experiment to Detect the Global EoR Signature (EDGES) is an experiment and radio telescope located in a radio quiet zone at the Murchison Radio-astronomy Observatory in Western Australia. It is a collaboration between Arizona State University and Haystack Observatory, with infrastructure provided by CSIRO.[1] EoR stands for epoch of reionization, a time in cosmic history when neutral atomic hydrogen gas became ionised due to ultraviolet light from the first stars.
Low-band instruments
The experiment has two low-band instruments, each of which has a dipole antenna pointed to the zenith and observing a single polarisation.[2] The antenna is around 2 by 1 metre (6.6 ft × 3.3 ft) in size, sat on a 30 by 30 metres (98 ft × 98 ft) ground shield. It is coupled with a radio receiver, with a 100m cable run to a digital spectrometer.[1] The instruments operate at 50–100 MHz (6.0–3.0 m), and are separated by 150m. Observations started in August 2015.[2]
In 2023, a new version of the low-band antenna in which the electronics are built into the antenna was installed on a larger ground plane of 50 x 50 metres (164 ft x 164 ft) to further reduce the effects of scattering from nearby objects and observations started in June 2023.[3][4]
78 MHz absorption profile
In March 2018, the collaboration published a paper in Nature announcing the discovery of a broad absorption profile centered at a frequency of [math]\displaystyle{ 78\pm1 }[/math]MHz in the sky-averaged signal after subtracting Galactic synchrotron emission. The absorption profile has a width of [math]\displaystyle{ 19_{-2}^{+4} }[/math]MHz and an amplitude of [math]\displaystyle{ 0.5_{-0.2}^{+0.5} }[/math]K, against a background RMS of 0.025K, giving it a signal-to-noise ratio of 37. The equivalent redshift is centered at [math]\displaystyle{ z\approx17 }[/math], spanning z=20–15. The signal is possibly due to ultraviolet light from the first stars in the Universe altering the emission of the 21cm line by lowering the temperature of the hydrogen relative to the cosmic microwave background (the mechanism is Wouthuysen–Field coupling). A "more exotic scenario," encouraged by the unexpected strength of the absorption, is that the signal is due to interactions between dark matter and baryons.[2][5]
In 2021, Melia reported that the deeper absorption is compatible with the alternative Friedmann–Lemaître–Robertson–Walker (FLRW) cosmology known as the Rh = ct universe.[6]
In 2022, an experiment called Shaped Antenna Measurement of the Background Radio Spectrum (SARAS) led by the Raman Research Institute reported that their measurements didn't replicate EDGES results rejecting them at 95.3% confidence level.[7][8]
High-band instruments
The high-band instrument is of similar design, and operates at 90–200 MHz (3.3–1.5 m).[2]
See also
- Large Aperture Experiment to Detect the Dark Ages (LEDA)
- Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE)
- List of astronomical observatories
- List of astronomical societies
- List of radio telescopes
References
- ↑ 1.0 1.1 "MIT Haystack Observatory: EDGES". https://www.haystack.mit.edu/astronomy/astronomy-projects/edges-experiment-to-detect-the-global-eor-signature/. Retrieved 2 March 2018.
- ↑ 2.0 2.1 2.2 2.3 Bowman, Judd D.; Rogers, Alan E. E.; Monsalve, Raul A.; Mozdzen, Thomas J.; Mahesh, Nivedita (1 March 2018). "An absorption profile centred at 78 megahertz in the sky-averaged spectrum" (in En). Nature 555 (7694): 67–70. doi:10.1038/nature25792. ISSN 1476-4687. PMID 29493587. Bibcode: 2018Natur.555...67B.
- ↑ Barrett, J.; Cappallo, R.; Wilson, K. (January 10, 2023). "MRO EDGES-3 Installation, November 2022; EDGES Memo #406". https://www.haystack.mit.edu/wp-content/uploads/2023/01/memo_EDGES_406.pdf.
- ↑ Rogers, Alan E. E.; Barrett, John P.; Bowman, Judd D.; Cappallo, Rigel; Lonsdale, Colin J.; Mahesh, Nivedita; Monsalve, Raul A.; Murray, Steven G. et al. (December 2022). "Analytic Approximations of Scattering Effects on Beam Chromaticity in 21‐cm Global Experiments" (in en). Radio Science 57 (12). doi:10.1029/2022RS007558. ISSN 0048-6604. https://onlinelibrary.wiley.com/doi/10.1029/2022RS007558.
- ↑ Barkana, Rennan (1 March 2018). "Possible interaction between baryons and dark-matter particles revealed by the first stars" (in En). Nature 555 (7694): 71–74. doi:10.1038/nature25791. ISSN 1476-4687. PMID 29493590. Bibcode: 2018Natur.555...71B.
- ↑ Melia, Fulvio (2021-03-15). "The anomalous 21-cm absorption at high redshifts" (in en). The European Physical Journal C 81 (3): 230. doi:10.1140/epjc/s10052-021-09029-4. ISSN 1434-6052. https://doi.org/10.1140/epjc/s10052-021-09029-4.
- ↑ Singh, Saurabh; Nambissan T., Jishnu; Subrahmanyan, Ravi; Udaya Shankar, N.; Girish, B. S.; Raghunathan, A.; Somashekar, R.; Srivani, K. S. et al. (2022-02-28). "On the detection of a cosmic dawn signal in the radio background" (in en). Nature Astronomy 6 (5): 607–617. doi:10.1038/s41550-022-01610-5. ISSN 2397-3366. https://www.nature.com/articles/s41550-022-01610-5.SharedIt
- ↑ Castelvecchi, Davide (2022-02-28). "Did astronomers see hints of first stars? Experiment casts doubt on bold claim" (in en). Nature. doi:10.1038/d41586-022-00577-7. PMID 35228734. https://www.nature.com/articles/d41586-022-00577-7.
External links
- Signal from age of the first stars could shake up search for dark matter - www.sciencemag.org
- Brubaker, Ben (2022-02-28). "Four Years On, New Experiment Sees No Sign of 'Cosmic Dawn'" (in en). https://www.quantamagazine.org/in-new-experiment-astronomers-see-no-sign-of-cosmic-dawn-20220228/.
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