Topic: Mid February Astronomy Bulletin

[Clive]

STARS DISAPPEAR BEFORE OUR EYES
NOIRLab

The night sky is getting progressively brighter: these are the findings of citizen-based science project, "Globe at Night", which is run by the National Optical-Infrared Astronomy Research Laboratory (NOIRLab) in the US. The research findings have revealed an increase in sky brightness of 9.6% per year between 2011 and 2022. This increase is due to 'skyglow', a form of light pollution resulting from the diffuse illumination of the night sky.

However, satellite results do not agree with the findings of this ground-based research project, indicating a lower increase of the night sky brightness, at about 2%. The main reason for this discrepancy is the inability of current satellite instruments to measure adequately wavelengths shorter than 500 nanometres. These wavelengths correspond to the bluer end of the visible spectrum and are major contributors to skyglow. In addition to this, satellites cannot measure light emitted in the horizontal plane, such as from windows or illuminated signs, so this added component to light pollution is entirely missed by satellite calculations. These two reasons highlight the need for ground-based observations and data input as seen by human eyes during the night, in order to be able to fully track the levels of light pollution.

The loss of dark skies is not only a big problem for ground-based astronomy but it also impacts humans and wildlife in major way. More specifically, the increasing brightness of the night skies disrupts the transition from night to day and by doing that, it also disrupts the biological systems that have evolved alongside this transition. Losing dark skies is also a cultural loss given how humanities stories and myths have always been linked to what we could see in the night sky.


FIRST KILONOVA PROGENITOR SYSTEM IDENTIFIED
NOIRLab

A kilonova - the merger of two neutron star companions - is a very rare event which produces heavy elements, including gold and silver. Such events are intricately linked to kilonova progenitor systems, themselves so rare that astronomers believe there are just about ten such systems in our Milky Way galaxy, out of at least one hundred billion stars that our galaxy hosts.

Now astronomers have detected the first progenitor system of a kilonova, using the SMARTS 1.5-metre Telescope at the Cerro Tololo Inter-American Observatory (CTIO). The system, called CPD-29 2176, lies about 11,400 light years away from Earth and comprises two stars, an ultra-stripped supernova neutron star and its massive companion, which is in the process of becoming an ultra-stripped supernova too.  A star can end its life by becoming an ultra-stripped supernova, an event where the star explodes and then has its outer layers stripped away by its companion star. Since the process lacks the energy of a typical supernova, the companion star remains in orbit around the neutron star, instead of being kicked out of the binary system.

The production of such a system is an unlikely process. A multitude of things have to happen, including the preservation of the binary system after the first explosion, the requirement that the second star will also become an ultra-stripped supernova and the necessity for the two neutron stars to finally merge together. This progenitor system appears to have all the necessary ingredients to undergo this long and rare process. The system is not only a very rare cosmic finding, but it will also improve scientific understanding of the poorly understood processes of creating some of the heaviest elements in the Universe.



ASTRONOMERS CONFIRM AGE OF THE MOST DISTANT GALAXY WITH OXYGEN
Nagoya University and the National Astronomical Observatory of Japan (RAS)

The arrival of the James Webb Space Telescope (JWST) has already led to a dizzying wealth of data including multiple detections of galaxies in the very early Universe. The first few weeks of JWST's operation, revealed many bright, very distant galaxies, challenging astronomers' understanding of how the earliest galaxies in the Universe were formed. An early galaxy will also be a very distant galaxy which means that light reaching us from such an object will have been stretched and shifted to the red end of the visible spectrum due to the Universe's expansion. However, this is not the only reason why a galaxy may appear red. For example, a galaxy very rich in dust will also appear red. In order to be certain that a galaxy is really distant or dusty, direct measurements of the galaxy's spectral lines are needed.

One such galaxy discovered by JWST is GHZ2/GLASS-z12. Astronomers at the Nagoya University and the National Astronomical Observatory of Japan immediately pointed the ALMA radio telescope in the direction of this galaxy to obtain emission lines of oxygen at the frequency suggested by JWST. Oxygen is abundant in distant galaxies and the team chose this particular element to increase the chances of detection. The observed redshift of the oxygen emission line confirmed that indeed this is a very distant galaxy (and not a dust-rich one), and is seen as it was 367 million years after the Big Bang. In the words of the team "The combined power of Webb and the radio telescope array ALMA give us the confidence to push our cosmic horizons ever closer to the dawn of the Universe."


DISTANT GALAXY MIRRORS EARLY MILKY WAY
Swinburne University in Australia / San Jose State University in the USA (RAS)

A galaxy has been discovered using data from the James Webb Space Telescope (JWST) which appears to resemble the Milky Way in its infancy. The galaxy, nicknamed "The Sparkler", is surrounded by globular clusters and satellite galaxies which it appears to be consuming over time. The galaxy is located in the constellation of Volans, at a redshift of 1.38. This means that what astronomers see today is an image of the galaxy nine billion years ago, at the early stages of its formation.

The Sparkler is home to around twenty-four globular clusters - dense collections of roughly a million stars. Examining the age and metallicity (the abundance of different elements in the stars that make up the clusters and the interstellar medium between them), revealed that the clusters appear to be younger versions of the globular clusters seen today in the Milky Way. The existence of a few clusters with intermediate ages and metal poor stars are indicative of a satellite galaxy being merged into the Sparkler. This is similar to what our own Milky Way has done in the past.

According to Professor Duncan Forbes, the discovery of this galaxy is the perfect opportunity to study the process by which a galaxy similar to our own can build up its mass, along with a window into how globular clusters are formed, something that has been somewhat of a mystery so far.


ESA'S CHEOPS FINDS FINDS AN UNEXPECTED RING AROUND DWARF PLANET QUAOAR
European Space Agency

ESA’s CHaracterising ExOPlanet Satellite (Cheops) mission has observed a dwarf planet at the outer edge of our solar system, which appears to have a ring orbiting it. The dwarf planet - Quaoar - belongs to a larger group of objects, known as trans-Neptunian objects (TNOs). Quaoar has a radius of about 555km and a small moon of about 80km radius, orbiting around it.

However, a series of observations between 2018 and 2021 also showed the existence of a ring made up of dense material orbiting the dwarf planet. The discovery was made by using data from the passing of the planet in front of a star, an event known as an occultation. Observing such events has increased mostly due the accurate star positions provided by Gaia. During an occultation, an object like a planet, passes in front of the star, producing a dip in the star's apparent brightness. In the case of Quaoar, smaller drops in brightness suggested there was material in a circular orbit around the TNO.

Other planets in our solar system have rings, with Saturn having the most impressive ring system of them all. However, what is special about Quaoar's ring, is the distance at which it is found. Any object with a significant gravitational field will have a limit within which any approaching celestial object will be pulled apart - this is known as the Roche limit. Rings are expected to be found inside the Roche limit; dense material outside that distance should coalesce into a moon within a short amount of time.

However, Quaoar's ring is found outside the TNO's Roche limit. This in itself means that the current thinking on how and where rings are formed needs to be revised. One potential explanation as to why the material hasn't formed a moon is that the temperatures are so low that they prevent the icy particles to actually coalesce. However, further investigations are needed in order to determine why Quaoar exhibits this characteristic.