Far out cosmology: Hubble constant confusion (Introduction)

by David Turell @, Saturday, February 09, 2019, 05:33 (190 days ago) @ David Turell

Still confused with several methods not agreeing:


"Something isn't quite right in the universe. At least based on everything physicists know so far. Stars, galaxies, black holes and all the other celestial objects are hurtling away from each other ever faster over time. Past measurements in our local neighborhood of the universe find that the universe is exploding outward faster than it was in the beginning. That shouldn't be the case, based on scientists' best descriptor of the universe.

"If their measurements of a value known as the Hubble Constant are correct, it means that the current model is missing crucial new physics, such as unaccounted-for fundamental particles, or something strange going on with the mysterious substance known as dark energy.


"To explain how the universe went from a tiny, hot, dense speck of soupy plasma to the vast expanse we see today, scientists have proposed what's known as the Lambda Cold Dark Matter (LCDM) model. The model puts constraints on the properties of dark matter, a kind of matter that exerts gravitational pull but emits no light, and dark energy, which seems to oppose gravity. LCDM can successfully reproduce the structure of galaxies and the cosmic microwave background — the universe's first light — as well as the amount of hydrogen and helium in the universe. But it can't explain why the universe is expanding faster now than it did early on.

"That means that either the LCDM model is wrong or the measurements of expansion rate are.
The new method aims to finally settle the expansion-rate debate,Simon Birrer, a researcher at the University of California, Los Angeles, and lead author on the new study, told Live Science.So far, the new, independent measurements confirm the discrepancy, suggesting new physics may be needed.

"To nail down Hubble's Constant, scientists had previously used several different methods. Some used supernovas in the local universe (the nearby part of the universe), and others have relied on Cepheids, or types of stars that pulsate and regularly flicker in brightness. Still others have studied the cosmic background radiation.

"The new research used a technique that involves light from quasars — extremely bright galaxies powered by massive black holes — in an effort to break the tie.


"Quasars don't usually shine steadily like many stars. On account of material falling into their central black holes, they change in brightness on scales of hours to millions of years. Thus, when a quasar's image is lensed into multiple copies with unequal light paths, any change in the brightness of the quasar will result in a subtle flickering between the copies, as light from certain copies takes a touch longer to reach Earth.

"From this discrepancy, scientists could precisely determine how far we are from both the quasar and the intermediary galaxy. To calculate the Hubble Constant, astronomers then compared that distance to the object's redshift, or the shift in wavelengths of light toward the red end of the spectrum (which shows how much the object's light has stretched as the universe expands).


"'Images of quasars that appear four times are very rare — there are maybe only 50 to 100 across the whole sky, and not all are bright enough to be measured," Birrer told Live Science. "Doubly- lensed systems, however, are more frequent by about a factor of five."

"The new results from a doubly-lensed system, combined with three other previously measured quadruple-lensed systems, put the value for the Hubble Constant at 72.5 kilometers per second per megaparsec; that's in agreement with other local universe measurements, but still around 8 percent higher than measurements from the distant universe (the older, or early, universe). As the new technique is applied to more systems, researchers will be able to home in on the exact difference between distant (or early) universe and local (more recent) universe measurements.


"Accurately measuring the Hubble Constant helps scientists understand more than just how fast the universe is flying apart. The value is imperative in determining the age of the universe and the physical size of distant galaxies. It also gives astronomers clues as to the amount of dark matter, and dark energy, out there."

Comment: the Hubble is still in trouble. Once inflation stopped (if it existed, which still seems likely) why did slow expansion persist? Answers await.

Complete thread:

 RSS Feed of thread

powered by my little forum