24.06.2017 change 14.11.2017

Tanning in protostars?

Photo: Fotolia Photo: Fotolia

Is it possible to get a tan around a young star called a protostar? Dr. Agata Karska from the Nicolaus Copernicus University Toruń Centre for Astronomy characterizes UV radiation around young stars to understand its importance for the process of star and planet formation.

Astrochemists seriously wonder whether or not protostars sunbathe, or whether there is UV radiation similar to that in our solar system in their vicinity. Although young stars do not produce large amounts of UV radiation, it can be generated in the vicinity of the star.

Knowing how stars and their planetary systems form allows to imagine the distant history of the Earth. Dr. Karska attempts to understand the role of UV radiation, which has so far seemed to be elusive and - perhaps - explain a few important mysteries concerning the formation of stars and extrasolar planets. Her research is funded by a three-year grant from the National Science Centre.

According to Dr. Karska, protostars, which in the future will begin to draw energy from fusion and become "real stars", are formed in the clouds of dust and gas that are impermeable to visible light. Hence the problem with observations. They should be observed in longer electromagnetic waves, preferably in far infrared. That is where both maximum dust brightness and key molecular transitions are that can be used to measure the temperature and density of gas in the immediate vicinity of the protostar.

However, the Earth\'s atmosphere strongly absorbs infrared radiation. Until recently, the only available observations were from balloon experiments or small space satellites. Infrared observations groundbreaking for the understanding of star formation have been made by the Herschel Space Observatory in 2009-2013.

Herschel observations have shown that there are many dynamic processes surrounding the formation of young stars. The dominant influence are the shocks accompanying jets and star winds. However, the shock models used so far cannot reproduce the abundance of various molecules (such as water and molecular oxygen) in the protostar environment.

"To solve this problem, Prof. Michael Kaufman from the US created new shock models that take into account the possible effects of ultraviolet radiation on the physics and chemistry of matter through which the shock wave passes. The first comparisons of these models to far-infrared observations of protostars are surprisingly consistent and allow you to determine the amount of UV radiation" - explained Dr. Karska.

In her project, the researcher characterises UV radiation around the protostars. The analysis includes temperature increases and changes in chemical composition of matter. This is especially important because it is from this matter that future solar systems similar to the Solar System will emerge. UV radiation can, for example, destroy water, which then will no longer be in the composition of the planets.

"Astronomers have noticed that much less stars are born than the amount of available matter would suggest. Star formation models show that this can be caused by UV radiation - Which is why understanding it is so important" - the researcher emphasised.

She noted that large amounts of interstellar dust make direct measurements impossible, so the researcher must use indirect methods. She will compare spectra of protostars from Herschel to a new generation of shock models that take into account the effects of UV radiation. The test for this method will be the observation of two molecules (hydrogen cyanide and cyanide), the relative amounts of which allow to determine the amount of UV radiation.

Observations of protostars in the lines of these molecules have been made with the 30 m IRAM telescope, which observes waves slightly shorter than 1 mm. Such observations can be made from Earth\'s surface only in very good weather and in optimum conditions. In this case, it is the Sierra Nevada mountain range in Spain at an altitude of almost 3000 meters above sea level.

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