JWST discovers tiny asteroid

I've been talking about asteroids so much recently. Anyways -- a paper published by Müller et al reveals the smallest object discovered by JWST so far. Müller et al went into the JWST data archives (which you can also access here) as they were interested in studying main-belt asteroids. In particular, while analysing asteroid 10920 (1998 BC1) with diameter 14.5-16.5km, they noticed an even smaller asteroid in the background with an estimated diameter of around 100m! In other words, an object as small as the International Space Station almost 3AU from the Sun was spotted by JWST. Pretty incredible!

JWST: 50,000 galaxies in Pandora's Cluster

NASA's JWST has unveiled a new deep field image showcasing unprecedented details in Pandora's Cluster (Abell 2744), as seen in the image above. The image captures three galaxy clusters, which are already massive, coming together to form a megacluster. The combined mass of these clusters produces a strong gravitational lens, naturally magnifying the effect of gravity. This enables distant galaxies from the early universe to be studied with greater precision by using the cluster as a magnifying glass. The white/yellow galaxies are closer to us, while those redder in colour are distant/background galaxies -- their light is super redshifted so we can only detect them at the upper limits of infrared. 

Spectrum of GNz-11

The galaxy GNz-11 was discovered by the Hubble Space Telescope in 2015. Back then, it was the most distant galaxy known to us, with its light travelling for 13.4 billion years; i.e., we're seeing GNz-11 as it was only 400 million years after the big bang! In February, a paper detailing the spectrum of GNz-11 using JWST dropped. In figure 1, we can see a dramatic drop off in flux at approx 1.5 microns known as the Lyman-α break. This happens due to hydrogen gas absorbing light at a very specific wavelength -- the break where we have the first drop off marks the point at which the light first encountered a clump of hydrogen gas in the universe. By comparing the wavelength this break appears at to the wavelength we know the Lyman-α to occur, we can figure out how much the light has been redshifted by, giving us the distance of GNz-11. This method actually resulted in GNz-11 being dethroned as the most distant galaxy, with recent JWST data revealing galaxy GNz-13 as the new most distant galaxy.

Figure 1 also shows emission lines at certain wavelengths (you can see these by looking out for the spikes/sudden increases in flux), giving us another *more precise* proxy to determining galactic redshift. From this, Bunker et al calculated GNz-11 to be at a redshift of 10.6034, slightly lower than the Hubble estimate of 10.957. Emission lines give also give us a lot of information about the galaxy itself, such as: the composition, the ratio of elements, and energy sources. From GNz-11's spectra we see some rare nitrogen emission lines, which are more intense than its oxygen emission lines, suggesting that nitrogen is more abundant than oxygen in the galaxy.

Oxygen and nitrogen are both created through fusion processes in stars, but oxygen is created at a higher rate than nitrogen due to its lower nuclear binding energy per nucleon. In addition, oxygen is more stable than nitrogen, allowing it to be created through more fusion pathways. Based on this, we would expect oxygen to be created before nitrogen in the universe. GNz-11's emission spectra seems to contradict this.

Black holes and dark energy

Could black holes be responsible for the accelerating expansion of the universe? Two papers published in the last month seem to imply so -- A Preferential Growth Channel for Supermassive Black Holes in Elliptical Galaxies at z<2 (Farah et al) and Observational Evidence for Cosmological Coupling of Black Holes and its Implications for an Astrophysical Source of Dark Energy (Farah et al).

The fact that the universe is expanding has been known for quite some time now. Space has stretched more than expected and it's theorised that this is accelerating expansion is due to "dark energy". Just to put things into context, it's estimated that universe is made up of 5% normal matter (the matter we can actually see with our eyes), 26% dark matter, and 69% dark energy. We call it "dark" because it cannot be directly detected or observed using current technology, but its existence is inferred from the way it affects the motion of galaxies and other cosmic structures. The exact nature of dark energy is still not well understood. 

Over the years, numerous hypotheses have been put forward to explain this accelerating expansion/dark energy. Many astrophysical papers claim that black holes could be the cause of acceleration; this all comes back to the question of "what is beyond a black hole's event horizon?". Within the event horizon, not even light can escape, so there's no current way for us to understand black holes completely. The best mathematical model we currently have is known as the Kerr model, which proposes a "singularity" at the centre of the black hole which harnesses all of its mass and resists the inward force of gravity. Another idea is that of "vacuum energy" within the black hole counteracting the force of gravity. Vacuum energy refers to the energy inherent in space-time itself. If black holes do actually have this vacuum energy beyond their event horizon, then as the universe expands, so do black holes. In doing so, they gain more vacuum energy (10e−9 joules per cubic metre of space) and thus mass via the mass-energy equivalence principle E=mc². As the black hole grows in mass, space-time will become diluted (due to the conservation of energy) and cause a negative pressure pushing outwards (dark energy)!

In this theory, black holes and dark energy are thought of as "cosmologically coupled". Croker and Weiner published a pretty detailed paper on this idea in 2019 and they found that mass and expansion scale factor must be cubically related. Theoretically, this works beautifully. Experimentally testing this is a whole different story. The 2nd Farah et al paper I listed outlines a way to use observational data to test this theory, arriving at polynomial link of 3.11 (very close to the theorised value of 3). However, many scientists are skeptical of the conclusions drawn due to some major assumptions made in the paper regarding galaxy formation and evolution. They also critically oversimplify supermassive black hole growth, when in reality, we do not fully understand the mechanisms governing it.

published: 06/03/23 by kaan evcimen