OH G339.88-1.26

The Hubble Space Telescope has photographed a bright stellar nursery studded with dazzling infant stars. Taken using Hubble's Wide Field Camera 3 instrument, the image above captures a massive protostar called OH G339.88-1.26 hiding behind star-forming clouds of dust and gas. The protostar lies an estimated 8,900 light-years from Earth in the constellation Ara.

During the protostellar phase, stars are still in the process of gathering mass from their parent molecular cloud. Despite its young age, OH G339.88-1.26 is estimated to be 20 times the mass of the Sun! As this protostar grows up, lives its life, and eventually dies, it will leave behind a black hole, annihilating those around it.

M51 - Whirlpool Galaxy

M51 lies about 27 million light-years away from Earth in the constellation Canes Venatici. The image above is a composite image that integrates data from JWST's Near-InfraRed Camera (NIRCam) and Mid-InfraRed Instrument (MIRI).

In the image, the dark red regions represent the filamentary warm dust permeating the medium of the galaxy. The red regions show the reprocessed light from complex molecules forming on dust grains, while colours of orange and yellow reveal the regions of ionised gas by the recently formed star clusters. I also captured a photo of M51 last November in the optical band; by comparing the two, you can truly appreciate how amazing JWST is!

Water vapour in PDS 70

A paper released in late July claims to have found water vapour in the terrestrial planet-forming zone of the the protoplanetary disk PDS 70. If you've never heard of the term, protoplanetary disks are disks which form around young stars and it's where planets form.

This discovery is part of a larger JWST study examining protoplanetary disks. The PDS 70 system is pretty unique as it has both an inner and outer protoplanetary disk (so 2 in total), separated by a gap of 8 billion kilometers! Perotti et al. found signatures of water vapour by analysing spectra in the inner protoplanetary disk, meaning that any rocky planets forming within that inner disk will have access to water as they form. This discovery is especially exciting because this inner disk extends to about 160 million kilometers away from its star, and the Earth orbits the Sun at an average distance of about 150 million kilometers away - i.e, a planet formed within this inner disk would be created in a similar environment to the one which created our planet!

Has JWST found supermassive dark matter stars?

In other news, Ilie et al. claim to have found candidate 'supermassive dark stars' in JWST data. Supermassive dark stars are hypothetical stars powered by dark matter rather than ordinary matter and can theoretically outshine entire galaxies!

Dark matter only interacts with the gravitational field – it cannot be directly seen, but its effects can, which is why we label it as 'dark'. Instead of being powered by nuclear fusion (like in regular stars), dark matter stars are powered by something known as 'dark matter annihilation', which is the process of a dark matter particle colliding with its corresponding antiparticle, releasing a lot of energy in the process. There is currently only one research group working on this 'dark matter star' theory, so it's still early days.

So if we cannot directly observe dark stars, how do we know they exist? The surroundings of such a star would be glowing as the local hydrogen and helium are heated by the local energy exchange taking place. We can, therefore, use spectra to dissect what elements exist in the region. 

The very first stars to have formed in our universe will have been responsible for turning the universe from opaque to transparent in a process known as reionization. If dark stars existed in this early period of the universe, they could've possibly been responsible for this reionization process. The most likely candidate for reionization, however, are what's known as 'Population III' stars – the oldest generation of stars in our universe currently being hunted by JWST. A Population III star going supernova would then enrich the universe with the heavier elements needed to form the stars and galaxies we see today. There are actually some papers which claim to have already found these Population III stars using JWST, but they're still being refereed (peer reviewed, etc). Luckily, a theoretical spectrum of a dark star vs. a bunch of Population III stars look very different from one another, so we should hopefully have more clarity on this topic soon.

Evidence against the dark matter model?

And for our last story – a paper released this month claims to have found strong evidence for an alternative theory of gravity known as MOND. This paper is making a lot of noise in the physics community, so let's have a look!

What is MOND? MOND essentially involves taking Newton's laws of gravitation and dynamics (which you might've learned in school or college) and tweaking them slightly to account for low acceleration regimes due to gravity. Einstein's theory of relativity is currently the most accepted theory of gravity, and all the tests we've performed on his theory so far have passed with flying colours. A consequence, however, of this theory is that it tells us that there is more mass in the universe than we can actually measure visibly (which is where dark matter and dark energy come in); visible matter only makes up about 5% of the universe's mass. At low accelerations, dark matter dominates.

It was proposed in 2012 to use binary star systems to test the theory of MOND as accelerations in these systems are sufficiently low enough. A year later, ESA launched their GAIA mission which measured properties of over a billion stars in our Milky Way galaxy to super high precision. The recent results published by Professor Chae plotting the binary separation against the orbital velocity showed that the GAIA data fit the (AQUAL) MOND model best at low accelerations. There are some issues, however, because the results don't really take some unknown factors into account, such as eccentricity and inclination. There are rumours of a paper in the works which uses more advanced statistical techniques to help combat these unknowns – interesting times ahead! :)

published: 03/09/23 by kaan evcimen