Astronomers usually get to hear from the far-off galaxies through high energy radiations like X-rays. It is extremely uncommon to receive relatively lower energy UV radiation from ancient galaxies like AUDs01. Such low energy photons usually get absorbed on the way or by the earth’s atmosphere. "Хъбъл" Космос Telescope (HST) has been very helpful in avoiding effects of earth’s atmosphere but even HST could not detect signal from this галактика probably due to noise.
Сега, ултравиолетовите изображения телескоп on Indian satellite AstroSat has detected extreme UV light for the first time from the галактика AUDFs01 situated 9.3 billion light-years away from Earth which is remarkable1.
Днес можем да разгледаме вселена и виж звезди намлява галактики формирана преди милиарди години, защото междугалактическата среда е прозрачна за светлината. Не беше така през първите няколкостотин милиона години след Големия взрив. Периодът, наречен от астрономите космически тъмни векове, е времето, когато междугалактическата среда е пълна с неутрален газ, който абсорбира фотони с висока енергия и прави вселена opaque to light waves. It was the period starting from the time when cosmic microwave background radiation emitted up to the time when first звезди намлява галактика were formed. The вселена then entered into what is called the Epoch of Reionization, when the dark matter started to collapse due to its own gravity and eventually started forming the звезди and the galaxies.
Космолозите се позовават на червеното отместване z, за да обозначат космическа епоха. Настоящото време се означава с z=0 и колкото по-висока е стойността на z, толкова по-близо е до Големия взрив. Например z=9 означава време, когато вселена was 500 million-year-old and z=19 when it was only 200 million-year-old, near Dark Age. At higher z values (z ≥ 10) it becomes extremely difficult to detect any object (star or галактика) due to sharp decline in inter galactic medium transmission. Scientists have been able to observe quasars and the galaxies up to z approximately equal to 6.5. Theories suggest that the звезди and the galaxies could have been formed much earlier at say higher z values and with advancement in technology we should be able to detect fainter objects at higher z values also [2]. However, most of the detection of galaxies are limited to approximately z=3.5 and are detected in the X-rays range. It is extremely difficult to detect the stars and galaxies in the extreme ultraviolet as it is heavily absorbed in the atmosphere.
Group of scientists led by Saha at Inter-University Centre for Astronomy and Astrophysics (IUCAA) were able to achieve this unique feat using Ultraviolet Imaging Telescope (UVIT) aboard the Indian satellite AstroSat . They observed the Галактика AUDFs01 located in the "Хъбъл" Extreme Deep field using extreme-UV light from the галактика. It could be possible because the background noise in the UVIT detector was much less than the ones on HST. The discovery is important as it opens up a new domain for detection of far off galaxies in the EUV range.
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Литература:
- Saha, K., Tandon, S.N., Simmonds, C., Verhamme, A., Paswan A., et al. 2020. AstroSat detection of Lyman continuum emission from a z = 1.42 галактика. Nat Astron (2020). DOI: https://doi.org/10.1038/s41550-020-1173-5
- Miralda-Escudé, J., 2003. Тъмната епоха на Вселената. наука, 300(5627), стр.1904-1909. DOI: https://doi.org/10.1126/science.1085325
