How the study of ancient galaxies is upending modern cosmology
Cosmology is the science that studies the origin and evolution of the universe, from its very early beginning 13.8 billion years ago with the Big Bang through the present epoch and into the future. While centred on astronomy, it also incorporates the science of physics, in particular gravitational physics and particle or quantum physics, combining theoretical modelling of the very early universe's origin with observational effects of such phenomena as dark matter and dark energy.
One of the fundamental paradigms of modern cosmology is that galaxy formation is determined to a great deal by how dark matter (an enigmatic and invisible form of matter that makes up to an estimated 20 per cent of all matter in the universe) concentrates throughout the cosmos; it is believed that dark matter is the "cosmic glue" that permeates and binds galaxies together, and that it is responsible for the stellar seeding of the universe's earliest galaxies.
VERY EARLY GALAXIES
Cosmologists have known about and studied a number of very early epoch galaxies for years; however, due to the fact that the majority of them are too faint and too redshifted, they have proven extremely difficult to examine using ground-based spectrophy through Earth's atmosphere. They had to wait until they could get above the Earth's atmosphere to make their observations, an opportunity which presented itself with the Dec. 25, 2021, launch of the James Webb Space Telescope (JWST). Now situated at the L2 Lagrange Point (a stationary position in space relative to the Earth's orbit around the sun), the JWST has been using its Near Infrared Spectrograph (Nirspec) camera to photograph various celestial objects using multiwavelength imaging.
The JWST recently captured images of a very distant galaxy theorized to be more than 11.5 billion years old, making it one of the oldest galaxies in the known universe. Named ZF-UDS-7329, this ancient galaxy is twice as massive as the Milky Way galaxy. However, while the Milky Way galaxy took billions of years to achieve its size, ZF-UDS-7329, which appears to have ceased its stellar production processes soon after it was formed, grew to its massive size over a period of only a few hundred million years. How it achieved such a massive size is currently unknown.
SPECTRA OF STARS
Analysis of the spectra of the stars within ZF-UDS-7329 indicate that they formed approximately 1.5 billion years before the JWST captured image, meaning that these stars likely formed 13 billion years ago, within about the first 800 million years of the universe's current estimated lifespan of 13.8 billion years. Spectroscopic observations of ZF-UDS-7329 stars revealed a much deeper redshift (the increase in the wavelength and corresponding decrease in the frequency and photon energy of electromagnetic energy observed when an object is moving away from an observer) than typical, as well as features usually associated with much older stellar populations, thereby indicating that ZF-UDS-7329 formed at a very early point on the universe's timeline.
However, standard cosmological modelling suggests that, at this early stage of the universe's evolution, there was not (or, at least theoretically, should not have been) sufficient quantities of dark matter structures believed required to hold massive galaxies such as ZF-UDS-7329 together present during this time. Current cosmology theory holds that the first globules of stars first coalesced into proto-galaxies, then formed dwarf galaxies, and subsequently merged together into the larger galaxies seen today only after one billion to two billion years of the universe's life. If this theory is correct, then a massive galaxy such as ZF-UDS-1329 did not have adequate time to grow so huge during the early stages of the universe, and should therefore, theoretically, not exist.
ANCIENT GALAXIES
The JWST continues to find and study other distant massive galaxies across the cosmos, which, like ZFUDS-7329, are theorized to have formed within several hundred million years of the universe's Big Bang, and should therefore, likewise, not have had time to form. A recent discovery of six massive objects by the JWST, while believed to be galaxies, could also possibly be gigantic quasars (extremely luminous active galactic nuclei) or supermassive black holes. Higher spectral resolution observations of these six objects will be required to measure their elemental abundance, the stellar ages of their component stars, and to determine if they are, indeed, ancient galaxies.
EXPANDING THE BOUNDARIES
How these early ancient galaxies such as ZF-UDS-7329 formed so rapidly and without the aid of dark matter during the universe's earliest epoch is puzzling to cosmologists. Their very existence is at odds with existing cosmological paradigms. Their appearance is upending current cosmological theories and models respecting how the first matter in the universe formed, and how and when galaxies, particularly massive galaxies, formed.
At the very least, the study of these ancient galaxies is likely to result in revisions to, if not a complete rewrite of, the standard theoretical models of galactic formation, stellar populations and the role of dark matter (and possibly, dark energy) during the evolution of the early universe.
This is just another example of how science continues to expand the boundaries, not only with respect to what can be observed and studied in the cosmos, but also of our knowledge of the processes that gave birth to the universe, and which are guiding its evolution.
THIS WEEK'S SKY
Mercury (mag. -1.6, in Aquarius – the Waterbearer), Venus (mag. -3.9, in Capricorn – the Sea Goat), and Mars (mag. +1.3, in Capricorn) are all , once again, unobservable this week, sitting, respectively, at 4 degrees, 2 degrees, and 1 degree above the southeast horizon at dawn.
Saturn (mag. +1.0, in Aquarius) and Neptune (mag. +8.0, in Pisces – the Fish) are likewise not observable, sitting 10 degrees and 6 degrees from the Sun at dawn, respectively.
Jupiter (mag. -2.2, in Aries – the Ram) becomes visible around 6:20 p.m., 46 degrees above the southwest horizon as dusk yields to darkness, before sinking toward the horizon, and setting shortly before midnight.
Look for the thin crescent Moon (complete with Earthshine — sunlight bouncing off the sun-lit side of Earth and hitting the unlit portion of the Moon)just below Jupiter on the evening of Mar. 12, just after sunset.
Uranus (mag. +5.8, in Aries) becomes visible 39 degrees above the western horizon, just to the upper left of Jupiter, around 10:20 p.m., before it, too, drops toward the southwest horizon, and sets about 12:20 a.m.
Until next week, clear skies.