Measuring the Universal Expansion Rate:


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Gravitational lenses measure universe expansion
by Bruno Van Wayenburg, Leiden Institute of Physics

It's one of the big cosmology debates: The universe is expanding, but how fast exactly? Two available measurements yield different results. Leiden physicist David Harvey adapted an independent third measurement method using the light warping properties of galaxies predicted by Einstein. He published his findings in the Monthly Notices of the Royal Astronomical Society.

We've known for almost a century about the expansion of the universe. Astronomers noted that the light from faraway galaxies have a lower wavelength than galaxies close by. The light waves seem stretched, or redshifted, which means that those far galaxies are moving away.

This expansion rate, called the Hubble constant, can be measured. Certain supernovas, or exploding stars, have a well-understood brightness; this makes it possible to estimate their distance from Earth and relate that distance to their redshift or speed. For every megaparsec of distance (a parsec is 3.3 light-years), the speed that galaxies recede from us, increases with 73 kilometers per second.

more at link................
[Just a pedantic whinge that annoyed me somewhat...the word highlighted in red "lower" should preferably be "shorter"]

the paper:

A 4 per cent measurement of H0 using the cumulative distribution of strong lensing time delays in doubly imaged quasars

Another article from same place on same subject.............

Gravitational lenses could hold the key to better estimates of the expansion of the universe:

If everything lines up just right, a galaxy’s gravitational pull can bend light from a distant quasar into four separate images. And if the light that forms those images has reached us along paths of slightly different lengths, researchers can measure the time delays between the paths and infer distances to the galaxy and the distant quasar. (Illustration: Martin Millon/Swiss Federal Institute of Technology Lausanne. Credit: Galaxy and quasar image: Hubble Space Telescope/NASA

The universe is expanding but astrophysicists aren't sure exactly how fast that expansion is happening—not because there aren't answers, but rather because the answers they could give don't agree.

Now, Simon Birrer, a postdoctoral fellow at Stanford University and the Kavli Institute for Particle Physics and Astrophysics at the Department of Energy's SLAC National Accelerator Laboratory, and an international team of researchers have a new answer that may, once refined with more data, help resolve the debate.

That new answer is the result of revisiting a decades-old method called time-delay cosmography with new assumptions and additional data to derive a new estimate of the Hubble constant, a measure of the expansion of the Universe. Birrer and colleagues published their results November 20 in the journal Astronomy and Astrophysics.

"It's a continuation of a large and successful decade-long effort by a large team, with a reset in certain key aspects of our analysis," Birrer said, and a reminder that "we should always reconsider our assumptions. Our recent work is exactly in this spirit."

more at link....

the paper:
Wrong also. Wavelengths are stretched longer in general for light received from more distant galaxies. That's what cosmological redshift means.
Yes, of course! Thank you q-reeus. The lower sort of threw me.
Redshift is of course longer wavelengths. Still I take it you agree with my point.