Friday, April 21, 2023

3964 - ASTRONOMY - gives us amazing science?

 

-   3964 -   ASTRONOMY  -  gives us amazing science?   -  December, 2022, astronomers using the Atacama Large Millimeter / submillimeter Array (ALMA) confirmed the discovery of one of the most distant galaxies ever observed. The faint radio light ALMA captured began its journey to us when the universe was less than 360 million years old.


------------  3964  -  ASTRONOMY  -  gives us amazing science?

-   Astronomers can't directly measure the distance of galaxies billions of light years away. Instead, they measure what is known as “redshift”, or “z.” In this case, the team measured a particular wavelength of light emitted by oxygen known as OIII.

-

-    When we observe the OIII emission line in a lab here on Earth, it has a wavelength of 88 micrometers. The OIII line ALMA observed in this particular galaxy was much longer, about 1,160 micrometers. Since red light has a longer wavelength than blue light, we say the observed OII line is shifted to the red, or redshifted.

-

-    Given these two numbers, calculating z is easy. It is just the relative redshift of the observed light, So z = (1160—88)/88 = 12.2 The bigger the z, the greater the redshift, and z = 12.2 is the largest confirmed redshift of a galaxy so far.

-

-    There are two ways light from a galaxy can be redshifted. The first is known as the Doppler shift and is caused by the physical motion of a galaxy through space.

-

-    When a train speeds past you, its horn sounds higher as the train approaches you and lower as it passes you and rolls away. The sound waves are bunched up as the train moves toward you and have a higher pitch, and they are stretched out as the train moves away from you, thus a lower pitch.

-

-    The same thing happens with light. If a galaxy is moving toward us its light is blueshifted, and the light is redshifted if it's moving away from us.The second way redshift can occur is through “cosmic expansion”. The universe is expanding, and this means as light travels to us from a distant galaxy its wavelength is stretched out by the expansion of space.

-

-    The longer the light travels the more the light is stretched, so the more the light is redshifted. This is known as “cosmological redshift”. For distant galaxies, almost all the redshift we observe is cosmological. This is how we know high redshift galaxies such as this one are very, very far away.

-

-   The rate of cosmic expansion is known as the “Hubble parameter”. The Planck mission observations of the cosmic microwave background put the value at about 68 (km/s)/Mpc, while observations of the Hubble and Gaia spacecraft give it a higher value of about 72 (km/s)/Mpc.

-

-   How long the light traveled from the galaxy to reach us is known as the light travel time and turns out to be about 13.1 billion years. Since the universe is about 13.46 billion years old, that means the light left the galaxy when the universe was about 360 million years old.

-

-    Since the light traveled for 13.1 billion years, does that mean the galaxy is 13.1 billion light-years away? Not quite. Because of cosmic expansion, the light traveled for much longer than it would have if the universe wasn't expanding. The galaxy was closer to us when the light began its journey. Much closer. If we calculate how far away the galaxy was from us 13.1 billion years ago, we get 2.4 billion light-years. So this galaxy was only 2.4 billion light years away, but the universe expanded so much that its light took 13.1 billion light-years to reach us.

-

-    The galaxy was 2.4 billion light years away, but once the light started heading our way the galaxy continued to move away from us because of the ever-expanding universe. So where is the galaxy now? It turns out the galaxy is now about 32 billion light-years away.

-

-     How can we see a galaxy 32 billion light-years away if the universe is less than 14 billion years old? The answer is that we can't. ALMA's view of the galaxy is how it looked when it was only 2.4 billion light-years away. We will never be able to see what the galaxy looks like now. It is too far away, and the universe is expanding too quickly for that light to reach us. We only see the optical echo of where it was and how it used to appear.

-

-    The James Webb Space Telescope has spotted some of the earliest and most distant galaxies.   Since it started delivering its first results in July, 2022, the James Webb has been supplying stunning images of the universe that include observations of the most distant and early galaxies we've ever seen.

-

-   Four of the most distant and thus earliest galaxies known to date, which existed when the 13.8 billion-year-old universe was no more than around 350 million years old.

-

-   And the James Webb isn't alone in spotting distant and early galaxies. In December, 2022, the Atacama Large Millimeter/Submillimeter Array (ALMA) spotted faint radio light from similarly ancient star groupings. This light began its journey to us when the universe was less than 360 million years old.

-

-    The link between time and distance in space comes from the fact that light doesn't travel instantaneously. Instead, light in a vacuum travels at a set speed of around 3.0 x10⁸ meters per second.

-

-    The sun is about 93 million miles or around 8.33 light minutes from Earth, meaning that we always see the sun as it was around 8 minutes and 20 seconds in the past. If the sun suddenly blinked out, Earth wouldn't slip into darkness for around 8 minutes. An observer on Uranus, which is almost 20 times farther away from the star than Earth, wouldn't notice for 2 hours and 40 minutes.

-

-    This travel time of light becomes really significant when we start to look out into the universe with powerful instruments like the JWST, ALMA, and the Hubble Space Telescope.   The most distant galaxy spotted by Hubble is GN-z11, which is located about 13.4 billion light-years away.

-

-    That means the light has been traveling to us for over 13 billion years and Hubble lets us see it as it was 300 to 400 million years after the Big Bang. A lot can happen to this light during its billions of years crossing the universe to reach us, and these effects are key to confirming the age and distance of these objects.

-

-    The universe isn't static, it is expanding and as this expansion progresses, the space between galaxies stretches.  Though light is made up of particles called photons, it also has a wavelike nature. Physicists refer to this dichotomy as "particle-wave duality.”

-

-     Like all waves, light has a wavelength — the distance between two "peaks" along the wave — and a frequency — the number of times a peak passes a set point every second — which are inversely proportional to each other and are connected to the energy the light carries.

-

-    Long-wavelength light, say radio waves, has a low frequency and low energy, while short-wavelength light, X-rays for example, has a high frequency and high energy. The electromagnetic spectrum runs from long-wavelength light like microwaves, radio waves and  infrared light to short-wavelength light like X-rays and gamma rays, the most energetic form of light.

-

-   The expansion of the universe is causing galaxies to recede away from each other, with more distant objects moving away more rapidly. This results in the wavelength of light being "stretched" out toward the longer, redder, frequencies of the electromagnetic spectrum. This is "redshift."

-

-    The more distant the galaxy, and thus the further back in time it is, the more shifted its originally visible light is down to near-infrared or even infrared. This is why the JWST views the universe in infrared and near infrared; it is the best way to view very early and distant galaxies.

-

-    There is an important way of calibrating this method of measuring cosmic distances called spectroscopy which also reveals information about these early galaxies. Spectroscopy takes advantage of the fact that different chemical elements emit and absorb light at a specific wavelength. That means light from distant galaxies and stars carries the "fingerprint" of the elements they are composed of.

-

-    Scientists look at the wavelength of light an element such an oxygen emits and absorbs in a lab here on Earth and compare that with what they see in the universe. Oxygen causes a feature in light called OIII at a wavelength of 88 micrometers here on Earth. When ALMA looked at the spectra from a distant galaxy, astronomers saw OIII at a longer wavelength, 1,160 micrometers meaning it had definitely been redshifted.

-

-   From the difference in wavelength between the lab and the astronomical observation it's easy to calculate the redshift. So for this ALMA galaxy z = (1160–88)/88 = 12.2, this means the galaxy has a redshift of 12.2. With some clever mathematics, this value of z reveals that the galaxy is seen as it was when the universe was just 360 million years old.

-

-    The chemical fingerprint of distant galaxies can be used to confirm the time period at which galaxies are seen in another way.   The early universe was a sea of hydrogen and helium with just a smattering of heavier elements, which astronomers call "metals" like oxygen and nitrogen. These early stars in the first galaxies were "metal-poor " as there just wasn't much in the way of heavy elements for them to incorporate.

-

-    The first stars converted hydrogen to helium via nuclear fusion and then converted helium to heavier elements, and when they exhausted this nuclear fuel, they could no longer support themselves against the inward pressure of gravity. This triggered the core of these stars to collapse, causing massive supernova explosions that dispersed the forged heavy elements across their host galaxies.

-

-    The remains of these stars became the building blocks of the next generation of stars, which was richer in metals than the prior generation. The process continues to this day, creating stars and galaxies which are more metal-rich in every generation.

-

-    That means astronomers can look at the spectra of light from a galaxy to see how abundant in heavy elements it is to get a picture of the age of the universe at which it is seen. If it's lacking in metals, that confirms it's probably a galaxy in the early universe.

-

-    Some cosmic explosions from dying stars, Type Ia supernovas have a light output that is so uniform that they are referred to as "standard candles." That means looking at the redshift of spectra from these supernovas is a good way of calculating distance across the cosmos, and thus helps confirm how distant some galaxies are and how "recently" we are seeing them.

-

-    'Red shift' is a key concept for astronomers. The term can be understood literally,  the wavelength of the light is stretched, so the light is seen as 'shifted' towards the red part of the spectrum.

-

-    Light behaves like a wave, so light from a luminous object undergoes a Doppler-like shift if the source is moving relative to us. Ever since 1929, when Edwin Hubble discovered that the Universe is expanding, we have known that most other galaxies are moving away from us. Light from these galaxies is shifted to longer (and this means redder) wavelengths - in other words, it is 'red-shifted'.

-

-   Since light travels at such a great speed relative to everyday phenomena (a million times faster than sound) we do not experience this red shift in our daily lives.

-

-   The red shift of a distant galaxy or quasar is easily measured by comparing its spectrum with a reference laboratory spectrum. Atomic emission and absorption lines occur at well-known wavelengths. By measuring the location of these lines in astronomical spectra, astronomers can determine the red shift of the receding sources.

-

-   However, to be accurate, the red shifts observed in distant objects are not exactly due to the Doppler phenomenon, but are rather a result of the expansion of the Universe.   Doppler shifts arise from the relative motion of source and observer through space, whereas astronomical redshifts are 'expansion redshifts' due to the expansion of space itself.

-

-    Two objects can actually be stationary in space and still experience a red shift if the intervening space itself is expanding.

-

-    The behavior of light cannot be explained solely by models of particles or solely by models of waves. If light is a particle, then why does it refract when traveling from one medium to another? And if light is a wave, then why does it dislodge electrons? But all behavior of light can be explained by combining the two models: light behaves like particles and light behaves like waves.

-

-     Particles and waves are sometimes conceived as opposites, but they’re not.   Light is not the only thing that exhibits behavior of both particles and waves. Other quantum entities also have this behavioral duality, and wave-particle duality is a key focus of the study of quantum mechanics.

-

                   April 18, 2023         ASTRONOMY  -  gives us amazing science?        3964                                                                                                                        

----------------------------------------------------------------------------------------

-----  Comments appreciated and Pass it on to whomever is interested. ---

---   Some reviews are at:  --------------     http://jdetrick.blogspot.com ----- 

--  email feedback, corrections, request for copies or Index of all reviews

---  to:  ------    jamesdetrick@comcast.net  ------  “Jim Detrick”  -----------

--------------------- ---  Friday, April 21, 2023  ---------------------------

 

 

 

 

         

 

-

 

 

 

 

           

 

 

No comments:

Post a Comment