-
-
- It is the year 2020 and one of the biggest mysteries to have occurred over the past several decades is still little known. We live in one of many billions of galaxies and outside of our local groups of galaxies all these galaxies are accelerating away from us and each other.
-
- The acceleration itself is increasing in acceleration. It is caused by some unknown energy in our Universe called Dark Energy appears to occupy all of space.
-
- The counterbalance to this accelerating expansion is the gravity that is holding our local galaxies together. If the Universe were created from “nothing” these two energies should cancel out. “Mass” is only “concentrated energy” according to energy equals mass times 9*10^16. That number is the speed of light squared in meters^2 / second^2.
-
- But the strength of gravity decreases with distance. Dark Energy remains constant with distance. The expansion is going to win out. The math in all of this tells us that 75% of the mass / energy in the Universe Dark Energy and 25% is Dark Matter and Ordinary Matter. What percent of this total “Matter” is ordinary matter?
-
- By 1998 cosmologists had made a prediction about how much “ordinary matter” there should be in the universe. They came up with about 5% should be regular stuff that is everything we know and think we understand. and the 95% is a mixture of “dark matter” and “dark energy“. Neither of these “dark’ things are understood. We just believe they are out there. The math says so.
-
- But when cosmologists counted up everything they could see or measure at the time, they came up short of even this 5% number. By a lot. The sum of all the ordinary matter that cosmologists measured only added up to about 2.5%, not the 5% what the math said to be in the universe.
-
- This is known as the “missing baryon problem” and for over 20 years, cosmologists have looked hard and wide for this matter without success. “Baryon” is a classification for types of particles that encompasses protons and neutrons and electrons, the building blocks of all the “ordinary matter” in the universe. Everything on the periodic table and pretty much anything that you think of as the material universe is made of “baryons“.
-
- Cosmologists have surmised that dark matter must exist in order to explain these gravitational patterns in space. Dark matter makes up most of the matter of the universe with the rest being baryonic matter.
-
- In 1997, scientists used the ratio of heavy hydrogen nuclei, that is hydrogen with an extra neutron, to normal hydrogen to estimate that baryons should make up this 5% of the mass-energy budget of the universe.
-
- Other astronomers were reporting that a direct measure of baryons in our present universe, determined through a census of stars, galaxies, and the gas within and around them, added up to only half of this predicted 5%.
-
- Provided the law of nature held that matter can be neither created nor destroyed, there were two possible explanations for these missing baryons. Either the matter didn’t exist and the math was wrong, or, the matter was out there hiding somewhere and we have not found it.
-
- Remnants of the conditions in the early universe, like the “cosmic microwave background radiation“, gave scientists a precise measure of the universe’s mass in baryons. Their computer simulations from these measurements predicted that the majority of the missing matter was hiding in a low-density, million-degree hot plasma that permeated the universe. Plasma is another word for charged particles.
-
- This was termed the “warm-hot intergalactic medium” and nicknamed “the WHIM.” The WHIM, if it existed, would solve the missing baryon problem but at the time there was no way to confirm its existence.
-
- In 2001, another piece of evidence in favor of the WHIM emerged. A second team confirmed the initial prediction of baryons making up 5% of the universe by looking at tiny temperature fluctuations in the universe’s cosmic microwave background, the leftover radiation from the Big Bang.
-
- With two separate confirmations of this number, the math had to be right and the WHIM seemed to be the answer. Now cosmologists just had to find this invisible plasma that somehow permeated space.
-
- Over the past 20 years, many other teams of cosmologists and astronomers have brought nearly all of the Earth’s greatest observatories to the hunt. There were some false alarms and tentative detections of warm-hot gas, that they eventually linked to gas around galaxies. If the WHIM existed, it was too faint and diffuse to detect.
-
- An unexpected solution was found in “fast radio bursts”. Fast radio bursts (FRB‘s) are extremely brief, highly energetic pulses of radio emissions. Cosmologists and astronomers still don’t know what creates them, but they seem to come from galaxies far away.
-
- As these bursts of radiation traverse the universe and pass through gasses and the theorized WHIM, they undergo something called “dispersion“.
-
- The initial mysterious cause of these FRB’s lasts for less than a thousandth of a second and all the wavelengths start out in a tight chirp. Therefore we would expect all the wavelengths would arrive here simultaneously.
-
- But when radio waves pass through matter, they are briefly slowed down. The longer the wavelengths, the more a radio wave “feels” the matter. Think of it like wind resistance. A bigger car feels more wind resistance than a smaller car. Longer wave lengths experience slightly more resistance.
-
- The “wind resistance” effect on radio waves is incredibly small, but space is incredibly big. By the time an FRB has traveled millions or even billions of light-years to reach Earth, dispersion has slowed the longer wavelengths so much that they arrive nearly a second later than the shorter wavelengths.
-
- By measuring the spread of different wavelengths within one FRB, astronomers could calculate exactly how much matter, that is how many baryons, the radio waves passed through on their way to Earth.
-
- To precisely measure the baryon density, astronomers needed to know where in the sky an FRB came from. If they knew the source galaxy, they would know how far the radio waves traveled. With that and the amount of dispersion they experienced they could calculate how much matter they passed through on the way to Earth?
-
- It was 11 years later before telescopes improved enough to be able to localize the first FRB. In August 2018 this new telescope could watch huge portions of the sky, about 60 times the size of a full Moon, and it can simultaneously detect FRB’s and pinpoint where in the sky they come from.
-
- Once astronomers knew the precise part of the sky the radio waves came from, they could use the Keck telescope in Hawaii to identify which galaxy the FRB came from and how far away that galaxy was.
-
- The first FRB detected came from a galaxy that is about 4 billion light-years away from Earth.
-
- By July 2019, astronomers had detected five more events. Using these dispersion measures for these six FRB’s, they were able to make a rough calculation of how much matter the radio waves passed through before reaching earth.
-
- The data fall right on the curve predicted by the 5% estimate. They had detected the missing baryons in full, solving this cosmological riddle and putting to rest two decades of searching.
-
- The excellent correspondence confirmed the detection of all the missing matter.
This result, however, is only the first step. They were able to estimate the amount of baryons, but with only six data points, today they can’t yet build a comprehensive map of the missing baryons.
-
- They have proof the WHIM likely exists and have confirmed how much there is, but they don’t know exactly how it is distributed. It is believed to be part of a vast filamentary network of gas that inter connects galaxies termed “the cosmic web”.
-
- With about 100 more fast radio bursts cosmologists could build an accurate map of this cosmic web. We have much more to learn. Now you know how little I know. We are playing with low percentages here.
-
- June 26, 2020 2767
----------------------------------------------------------------------------------------
----- 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” -----------
- https://plus.google.com/u/0/ -- www.facebook.com -- www.twitter.com
--------------------- Saturday, June 27, 2020 -------------------------
-----------------------------------------------------------------------------------------
No comments:
Post a Comment