25 January 2018
An international team of astronomers, including two STFC scientists, have made the very first detection of a jet from a very young, massive star in a galaxy that is not our own.
The paper was co-authored by Pamela Klaassen, instrument scientist at the STFC’s Edinburgh site, the UK Astronomy Technology Centre (UK ATC), and UK ATC’s Head of Science Chris Evans.
Dr Klaassen said: “With this observation, we see that the details of star formation we see in our galaxy are also possible elsewhere, even when the conditions and material available are quite different to those we’re used to.”
Stars like the Sun are constantly forming in our galaxy and further afield in more distant galaxies. They form in predictable ways, emerging from their natal environment often surrounded by a system of planets which formed from a disk.
Stars with more mass, upwards of eight times that of the Sun, are much rarer and their formation remains something of a mystery. These more massive stars form deep within their natal clouds of gas and dust and are generally too obscured to be visible with optical telescopes. Under the right conditions, it is sometimes possible to see a jet or outflow of expelled gas, but only if it’s powerful enough to push out of the natal cloud. These narrow streams of gas move away from the forming star at high speeds – and often the bigger the star, the bigger and faster the jet.
Astronomical instruments like MUSE (Multi Unit Spectroscopic Explorer) on the European Southern Observatory’s Very Large Telescope (ESO VLT) in Chile are vital for understanding these jets of gas.
Dr Klaassen said: “In this paper, we present the first evidence for such a jet from a young stellar object in another galaxy, the nearby Large Magellanic Cloud (LMC).
“The LMC has a lower abundance of ‘metals’ (atoms heavier than hydrogen and helium) than our own galaxy, which means that the environment of the young star is less opaque than an equivalent region in the Milky Way helping make this detection robust.
“The jet spans about 36 light years (or 11 parsecs), which makes it among the largest jets of its kind ever found. The star powering the jet appears to be about 12 times as massive as the Sun, and its velocity structure was revealed by the high spectral resolution of MUSE – we know which part of the jet is angled towards us, and which is angled away.”
The data used for this work comes from the VLT in Chile’s Atacama Desert, which is among the largest optical telescopes in the world and is one of the most competitive telescopes on which to obtain precious observing time.
It is only with this kind of instrument that this could be done; regular instruments would not have detected the jet. The VLT can detect objects roughly four billion times fainter than can be detected with the naked eye.
The project team was led by Dr Anna McLeod from the University of Canterbury in New Zealand, who says this discovery will drive significant advancement in the field of star formation: “The formation mechanism of massive stars was predicted three decades ago and involved an accretion disk, similar to how their lower-mass siblings form. Over the years numerical simulations were produced which support this scenario. Recently there has been some initial observational evidence that this might indeed be the case. In our paper, we present compelling evidence that high-mass stars form in a similar way to Sun-like stars.
“We have detected a very young and still forming massive star – a so-called young stellar object – which is launching a bipolar jet. The jet is direct evidence for what we call an accretion disk, i.e. a disk around the equator of the star through which the star is gathering matter and thus growing, which is what we see in low-mass stars.”
This discovery brings direct evidence that massive stars up to 12 times that of our Sun form like low-mass stars.
More information is available on the University of Canterbury website.