Ken Tapping – August 5, 2022 / 4:00 am | History: 378743
Photo: Greg Reilly
A once-in-a-lifetime photo of a once-in-a-lifetime comet by a local South Okanagan photographer near Causton.
If you want to make a comet, asteroid, planet, star, or many other bodies, the recipe is the same. There is only one ingredient: cosmic clouds of gas and dust.
The procedure is the same, just collect some of the material in a lump. What you end up with depends entirely on how big a lump you work. The mass of the lump determines two critical quantities, the pressure and the temperature at the core of this body.
The temperature in the Earth’s core is about 5200 C and the pressure about 3.6 million times greater than the atmospheric pressure at the surface. The pressure comes from the weight of the overlying rock. The internal heat comes from two sources – the energy released by the impacts of incoming objects when the Earth formed, about 4.5 billion years ago, and from the decay of radioactive elements present in the cosmic material.
For a planet the size of ours, heat escapes very slowly. For smaller worlds, the process is faster.
Imagine that somewhere in a big cloud of cosmic gas and dust, a few grains wander into each other, and thanks to static electricity or something else, they stick together. The resulting grain is larger and presents a greater target for impact than other particles, so it has a better chance of capturing more particles. Even in these clouds, the density of material is very low, so collisions are rare, but there are many, many times.
As the grain grows, it samples all the chemicals that make up the cloud, including hydrogen and other volatiles. Eventually, it turns from a grain into a lump, and after more time becomes massive enough to take on a new force to hold the lump together and increase its growth rate by attracting more and more of the surrounding material: gravity.
The impact of new material on the growing clump makes it hot, melting it, so that when it gets big enough and its gravity strong enough, it is pulled into a sphere perhaps a thousand kilometers in diameter. Now that’s a big asteroid. Continued impacts produce more heat. Of course, the formation process can stop at any time, allowing the object to cool and eventually solidify. In our case, however, growth continues. When it reaches a diameter of several thousand kilometers, it has become a planet.
If our new planet is close enough to a star, the heat from the star will evaporate and expel most of the gas and other volatile material, so that we end up with a rocky planet, like Mercury, Venus, Earth, or Mars.
On the other hand, if the planet manages to hold on to its gas and volatiles, it can grow into a gas giant planet, like Jupiter, Saturn, Uranus, and Neptune. During their formation, these planets collected a huge amount of internal heat, so even today their cores are extremely hot.
Now things get really interesting. If our planet collects material to the point where it exceeds about 20 times the mass of Jupiter, the pressure and temperature in the core become high enough for some elements, such as deuterium and lithium, to undergo nuclear fusion, producing energy. It’s no longer a planet, and it’s not yet a star that gets its energy through hydrogen fusion.
Objects like this, not quite a graduated star, are known as brown dwarfs. These objects show some aspects of stellar behavior, such as flaring. Astronomers are very interested in them. If the material keeps coming and our star reaches 100 or more Jupiter masses of material, we have a new star.
It’s amazing what can be done with one recipe, one ingredient and just changing the amount.
•••
• Saturn rises soon after sunset, followed a few hours later by Jupiter. After another two hours or so, Mars creeps into view, followed, just as the sky begins to lighten for dawn, by Venus.
• The moon will be full on the 11th.
This article was written by or on behalf of an outside columnist and does not necessarily reflect the views of Castanet.
Ken Tapping – Jul 29, 2022 / 4:00 am | History: 377609
Photo: NASA
The James Webb Space Telescope
One of the goals of the James Webb Space Telescope is to find out how soon after the Big Bang galaxies began to form and when stars began to produce the elements needed to create planets and life.
JWST is only just getting into action, but it’s already giving us some strong hints. This kind of research is possible because looking at greater and greater distances takes us back in time. Although light travels extremely fast, cosmic distances are so vast that light from stars and galaxies can take anywhere from years to billions of years to reach us, depending on how far away they are.
Expressing such distances in kilometers results in extremely large numbers that are difficult to visualize. We often express these distances in “light years,” which is the distance light travels in one year. If we look at a galaxy a billion light-years away, we see it as it was when that light made its way to us a billion years ago.
By looking at increasingly distant objects, we see the universe as it was further back in its history. Telescopes are time machines. Recent observations using JWST show us that galaxies like ours existed only 600 million years after the Big Bang, just under 14 billion years ago.
The oldest and most distant thing we can see is the cosmic microwave background, or CMB. This dates back to about 380,000 years after the Big Bang, the beginning of the universe, about 13.8 billion years ago.
The CMB is basically a nearly uniform glow over the entire sky, emitted when the universe has expanded and cooled enough for light to pass through. However, when this aurora is mapped accurately, we see small temperature variations within it. They note the clumping of material collapsing under its own gravity, about to become the first galaxies.
When the universe became transparent, there were no stars to illuminate it. It was dark. We often refer to the period of time between the CMB and the first stars as the “cosmic dark age”.
We would really like to know when this epoch ended and the first stars and galaxies formed. We do this by using our ever-improving instruments to work our way out from Earth and back in time until we stop seeing galaxies or, hopefully, see the first galaxies and stars actually forming.
Of course, when we see one of these distant, faint galaxies, we need to know how far away it is, and thus how far back in time we are looking. Direct measurement of such vast distances is extremely difficult. Fortunately, there is a simple, fairly reliable indirect method. We use the expansion of the universe.
This has been accurately measured over decades of work. The rate at which a distant galaxy is moving away from us from the expansion of the universe is directly related to how far away it is. A galaxy that is twice as far away from us as another will be moving away twice as fast.
The relationship between recession rate and distance has been widely measured and is known as the Hubble constant.
Measuring the recession rate of a galaxy is relatively easy, so we apply the Hubble constant and have a very good idea of the distance of that galaxy. So the search is for ever fainter galaxies that are moving away from us at ever higher speeds, putting them at ever greater distances. This requires ever better telescopes, such as JWST.
JWST has just started operating, so the discovery of normal-looking galaxies existing only 600 million years after the Big Bang is encouraging. Their formation must have started very quickly. At this stage we don’t yet know how fast because we haven’t gone far enough back in time yet.
Watch this space.
•••
• Before dawn, Saturn lies low in the south, with bright Jupiter to the left, then Mars, and finally Venus, lying low in the dawn glow.
• The Moon will reach its first quarter on July 5.
This article was written by or on behalf of an outside columnist and does not necessarily reflect the views of Castanet.
Contributed – Jul 22, 2022 / 4:00 am | History: 376511
Photo credit: smithcube.wilsonema.com
The James Webb Space Telescope (JWST) is almost in its parking lot, 1.5 million kilometers from Earth.
It works perfectly and sends back beautiful images.
Its 6.5-meter mirror, made up of 18 hexagonal segments, is fully deployed, with all these segments positioned to millionths of a meter (the spacecraft had to be folded to fit inside the rocket).
The mirror is larger than that of the Hubble Space Telescope (HST); it can collect about seven times more light and distinguish finer details. It will supplement rather than replace the HST.
Instead of observing visible light, which is HST’s purpose, JWST will observe mainly at infrared wavelengths. This makes it better for looking at the formation of stars and planets and for exploring the outermost regions of the universe.
Setting up telescopes in space is a lot of work and expensive, and no one will be around if something goes wrong during setup.
HST’s problems were solvable because its low orbit made it accessible by the Space Shuttle. We currently have no easy way to get a service engineer on the James Webb Space Telescope.
Ground-based telescopes can be made larger, and telescope instruments can be easily changed to keep up with evolving scientific needs. If something breaks, it can be fixed. So, given the enormous additional costs and challenges involved in putting telescopes in space, why do we do it?
If you look at a star through a telescope, most nights you will see a spot dancing around and flashing different colors while you should be seeing a colored dot. The moon and planets can…
Add Comment