Why some galaxies 'die' and others do not

Dying galaxies

Photo: Pixabay

Nothing lasts forever, even galaxies, and maybe even universes.

The James Webb Space Telescope has just observed the oldest dead galaxy, that is, one in which the birth of new stars has ceased. This galaxy, poetically named RUBIES-UDS-QG-z7, ceased producing stars a mere 700 million years after the Big Bang.

Our galaxy, the Milky Way, formed some 13.6 billion years ago, some 200 million years after the Big Bang, and is still vigorously forming new stars.

The key substance driving the formation of stars, galaxies and ultimately planets and life, is hydrogen. When the universe cooled, it was made up almost entirely of hydrogen. In the young universe something stirred up the hydrogen clouds so they collapsed to form galaxies, and within those galaxies, they further collapsed to form stars.

Nuclear fusion in the cores of those stars produced energy and the first starlight, and, as waste products, all the other elements needed for making planets and living things. As time passed, galaxies merged and formed bigger ones, which stirred up the hydrogen clouds, triggering the formation of new generations of stars. Since hydrogen is a resource that is used up in forming stars, and on a smaller scale, water and other chemicals found in space, on planets and in living things, it has to run out at some point.

When that happens, star formation ceases and the galaxies are described by astronomers as "dead". That raises an intriguing question. Why is our galaxy—along with the billions of others our telescopes show us that formed around the time RUBIES-UDS-QG-z7 was producing stars—still producing stars, while some galaxies, like RUBIES-UDS-QG-z7 are long dead?

The total mass of all the stars in our galaxy is something like 300 billion times the mass of the Sun. RUBIES-UDS-QG-z7 was bigger, containing a total mass of stars equal to some 15 billion solar masses. With all that mass, we would expect to see that galaxy still vigorously forming stars today. That underlines the fact we have a lot to learn about the birth and evolution of galaxies.

In the young universe, stars were more massive, which means they were enormously brighter than the Sun and enjoyed active but very short lives before collapsing and exploding. The waste products produced during their short lives of energy production, together with elements produced in the explosions seeded the young universe with the ingredients for making planets and life. Interestingly, those ingredients can strongly affect subsequent generations of stars.

The first stars formed from more or less pure hydrogen. However, after a few generations of bright, short-lived stars, the hydrogen clouds came to contain small but important concentrations of the other elements. This significantly affected the stars that formed from them. They were cooler, redder and were less bright, which means they used their hydrogen fuel more slowly and so had much longer lives, providing time for life to develop on our world and almost certainly on others.

That raises a big question. What was different about RUBIES-UDS-QG-z7?

It looks as though those first generations of bright, short-lived stars were not followed by dimmer, longer-lived stars. So, after 700 million years, the galaxy "died".

Maybe "dead" is the wrong word, because white dwarf stars—the remnants of "dead" lower mass stars—continue to shine for billions of years,and dim, red dwarf stars, which could have planets and life, can last almost as long.

Light and warmth can still be available long after star birth has ceased. Maybe "retired" is a better word.

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• Venus now lies very low in the east before dawn. After dark, Jupiter shines yellowish-white high in the west and red Mars is high in the southwest.

• The Moon will be new on April 27.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.

Advances in technology help us see more in the sky

The 'new' astronomy

Photo: DRAO

The Canadian Hydrogen Intensity Mapping Experiment at the National Research Council's Dominion Radio Astrophysical Observatory near Penticton is a revolutionary new Canadian radio telescope designed to answer major questions in astrophysics and cosmology.

The radio telescope at the Algonquin Radio Observatory, located in Algonquin Park, Ontario, is typical of the radio telescopes built around the world in the 1960s.

It is a spectacular instrument with a 46-metre dish. At an operating wavelength of 2.8 centimetres it can "see" a patch of sky about one tenth the diameter of the Moon in the sky.

That means that pointing the instrument at known cosmic sources of radio waves and measuring the strength and other properties of their radio emissions is quite easy. However, using it to map a large area of sky involves scanning the region of interest, measuring the radio brightness one "pixel" at a time.

Searching the sky for unknown, new objects would also be a very tedious process. The operating cost of large telescopes like that one does not encourage large-field mapping projects because of the time involved and largely rules out more speculative searches, making purely serendipitous discoveries rare.

There is always strong competition for observing time on the larger astronomical instruments and in general the proposals with the highest probability of getting results are the ones most likely to be accepted. Moreover, large, single-dish telescopes can usually be used for only one project at a time. In addition, until recently, the data obtained usually went home with the astronomer and after he or she was done with it, ended up stored on a shelf in their office. Back in the 1960s, that was usually in the form of stacked reels of magnetic tape.

Things are very different now. Let's look at the CHIME (Canadian Hydrogen Intensity Mapping Experiment) radio telescope, now operating at the National Research Council's Dominion Radio Astrophysical Observatory near Penticton, and the CHORD (Canadian Hydrogen Observatory and Radio transient Detector) radio telescope currently under construction. Both have a huge field of view—most of the sky over the observatory. Secondly, despite the very focussed-sounding names for these instruments, they can be used for many different experiments, often at the same time.

Whereas older radio telescopes could only accept a narrow band of wavelengths at a time, these instruments can grab a substantial chunk of the radio spectrum and digitize it. Once that is done, the data can be split among multiple channels of signal processing, each set up for a different experiment. It is possible to image different areas of sky and search for fast radio bursts and other things at the same time.

Another big difference is in the data that is recorded. In the past, due to the limited capacity of digital data handling and storage media, astronomers took home data that was mostly, or completely processed, which meant it was of limited use for any other projects. Today, we can handle almost unprocessed data, so after the intended information has been extracted, it is possible to search that data for other things.

Finally, the data is stored in large repositories, such as the Canadian Astronomy Data Centre, where it is available for use by other researchers. In some cases the data is private for a year or so, giving the astronomers who obtained it a chance to analyze it and to get their results into print first.

One possible downside in the new style of radio astronomy is we don't need to travel at those instruments, which are usually at exotic locations, to make the observations. However, the new form of astronomy provides much more efficient use of the money spent on building and operating observatories, and makes their scientific productivity higher than ever. That is exciting.

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• Venus now lies very low in the east before dawn. After dark Jupiter shines yellowish-white high in the west and red Mars is high in the southwest.

• The Moon will reach last quarter on April 20.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.

Another eclipse seen by radio

Radio astronomy in action

Photo: Contributed

The Dominion Radio Astrophysical Observatory near Penticton

Canadian radio astronomy started directly after the Second World War.

Arthur Covington, a scientist with the National Research Council, worked on radar development during the war and when peace came, he and his colleagues made Canada's first radio telescope out of spare radar bits and pieces.

The radio telescope had a small antenna and the only radio source our pioneers could detect was the Sun. However, the instrument could do no more than register an increase in the signal power being received when the antenna was pointed at the Sun.

It just measured the total amount of radio power coming from a patch of sky 10 or more times the diameter of the Sun. There was no way the instrument was capable of making a usable solar image.

That was a problem. Optical astronomers had long established most solar activity was concentrated in areas known appropriately as active regions, which contain sunspots and the other structures associated with solar activity. The pioneer radio astronomers were sure there was a contribution to the radio emission by the solar disc as a whole, but it was likely higher levels of radio emission were coming from the active regions. It was important to know that but the radio telescope was incapable of answering the question, or was it?

On Nov. 23, 1946, a rare opportunity offered itself. There was a solar eclipse that was visible in eastern Canada. Covington and his colleagues could use the eclipse to see where the radio emissions were coming from.

The concept was simple, track the Sun with the radio telescope and measure the changes in the strength of the received signal as the Sun was obscured by the Moon. As the Moon covered more and more of the disc, the signal level would fall. As the Moon moved on, the signal would rise again until it was back at the original level.

However, if there was a source of enhanced radio emission on the solar disc, there would be a sharp drop as the Moon covered it up. If the optical telescopes showed an active region or group of sunspots being covered up at the same time, one could conclude those enhanced radio emissions were coming from the active region.

That conclusion would be reinforced if the signal level rose again when the active region was uncovered. In that way, Covington and his colleagues showed that solar active regions were sources of radio emission.

Since solar active regions are a feature of solar magnetic activity, those radio measurements provided an objective, weather-independent stethoscope on the Sun. That led to a solar monitoring program that continues to the present day.

In 2018, we were in the process of "shaking down" a new solar radio telescope, the Next Generation Solar Flux Monitor, at the National Research Council's Dominion Radio Astrophysical Observatory near Penticton. The instrument was intended for monitoring solar activity as the driver for space weather, and was a joint project of the National Research Council, Natural Resources Canada and the Canadian Space Agency.

It just so happened that on Aug. 21, the observatory was close enough to the path of the eclipse for the Sun to be partially covered by the Moon. So we decided that repeating what Covington and his team did back in 1946 would be a good test of our new instrument.

Of course it was much easier for us because we just sat and monitored the eclipse while computers took charge of the radio telescope. Watching the strength of the radio emission dropping as the Moon covered the Sun, and the steep drops as active regions were covered was exciting. It gave us a hint of how Covington and his colleagues must have felt back in 1946.

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• Venus now lies very low in the east before dawn.

• After dark Jupiter shines yellowish-white high in the west and red Mars is high in the south.

• The Moon will be full on April12.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.

Looking back to the origins of the universe

Before the Big Bang

Photo: Pixabay

Einstein was not happy.

In the early years of the 20th century, he came up with his General Theory of Relativity, an important part of which was a suggested explanation of gravity.

Newton came up with the idea of gravity, but did not know what it was. Einstein was unhappy because his equations were telling him things he didn't like. Einstein believed the universe to be unchanging and eternal. His equations said that could not be the case. It had to either collapse or expand.

So, completely out of his imagination, he added a cosmic fudge factor, a force that would keep the universe static. He gave it the impressive name, Cosmological Constant, which would be represented by a capital Greek letter, lambda. As it turned out decades later, that would be useful.

Working independently, Georges LeMaitre, a senior Jesuit priest, was doing his own calculations, which told him the universe was expanding. However, he did not question his result and concluded billions of years ago the universe was concentrated in a tiny body, which he called the “Primaeval Atom".

He had the opportunity to seek out Einstein at a conference to discuss his work with the famous man. Despite the fact Einstein’s equations, before he added the fudge, predicted exactly what LeMaitre had found, Einstein crushingly told the priest, "your calculations are correct, but your physics is atrocious". Some time later, when it was discovered the universe was, in fact, expanding, Einstein finally apologized.

We now believe the universe started from something tiny, like LeMaitre's “Primaeval Atom,” which then, just under 14 billion years ago, started to expand and cool, leading to the universe we see around us today.

Fred Hoyle, a prominent sceptic of the idea that the universe had a beginning, derisively referred to that beginning as the "Big Bang.” Ironically, that name stuck. That idea raises a very intriguing question: What existed before the Big Bang? Is it possible to find out?

The problem is the conditions at the moment of the Big Bang were so extreme our current knowledge of physics breaks down. Amazingly, thanks to research using particle accelerators such as the Large Hadron Collider, which sits on the boundary between France and Switzerland, researchers have actually got to within a few microseconds after the Big Bang, when material was heated and compressed to an incomprehensible degree. However, for the time being, that is as far as we have been able to get.

One idea widely discussed is that of the “multiverse,” in which universes form and then dissipate like bubbles in foam. In that case, before the Big Bang there was the foam with its evolving universes as bubbles, with one about to become ours.

There may be a way to test this multiverse idea. In our bathtub foams, we get bubbles touching each other. The interface between those bubbles has a different shape. The idea is that if our universe is touching another, the differently shaped interface should be visible in the cosmic microwave background.

Measurements indicate our universe will keep expanding indefinitely, faster and faster, eventually becoming a starless, cold vacuum with scattered black holes. Over time they will evaporate, leaving a dark, cold emptiness.

According to physicist Roger Penrose and others, that will eventually fold back into a singularity, a primaeval atom, which at some point will start to expand, starting the whole thing over again.

•••

• Venus now lies very low in the pre-dawn glow.

• After sunset, Jupiter shines yellowish-white high in the southwest and red Mars is high in the south.

•The Moon will reach its first quarter on April 4.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.