New JWST Data Explores 'Hubble Constant' Tension for Universe's Expansion Rate (space.com) 9
"Scientists can't agree on the exact rate of expansion of the universe, dictated by the Hubble constant," a new article at Space.com reminds us:
The rate can be measured starting from the local (and therefore recent) universe, then going farther back in time — or, it can be calculated starting from the distant (and therefore early) universe, then working your way up. The issue is both methods deliver values that don't agree with each other. This is where the James Web Space Telescope (JWST) comes in. Gravitationally lensed supernovas in the early cosmos the JWST is observing could provide a third way of measuring the rate, potentially helping resolve this "Hubble trouble." "The supernova was named 'supernova Hope' since it gives astronomers hope to better understand the universe's changing expansion rate," Brenda Frye, study team leader and a University of Arizona researcher, said in a NASA statement.
This investigation of supernova Hope began when Frye and her global team of scientists found three curious points of light in a JWST image of a distant, densely packed cluster of galaxies. Those points of light in the image were not visible when the Hubble Space Telescope imaged the same cluster, known as PLCK G165.7+67.0 or, more simply, G165, back in 2015. "It all started with one question by the team: 'What are those three dots that weren't there before? Could that be a supernova?'" Frye said.
The team noted a "high rate of star formation... more than 300 solar masses per year," according to NASA's statement: Dr. Frye: "Initial analyses confirmed that these dots corresponded to an exploding star, one with rare qualities. First, it's a Type Ia supernova, an explosion of a white dwarf star. This type of supernova is generally called a 'standard candle,' meaning that the supernova had a known intrinsic brightness. Second, it is gravitationally lensed. Gravitational lensing is important to this experiment. The lens, consisting of a cluster of galaxies that is situated between the supernova and us, bends the supernova's light into multiple images...
To achieve three images, the light traveled along three different paths. Since each path had a different length, and light traveled at the same speed, the supernova was imaged in this Webb observation at three different times during its explosion... Trifold supernova images are special: The time delays, supernova distance, and gravitational lensing properties yield a value for the Hubble constant... The team reports the value for the Hubble constant as 75.4 kilometers per second per megaparsec, plus 8.1 or minus 5.5... This is only the second measurement of the Hubble constant by this method, and the first time using a standard candle.
Their result? "The Hubble constant value matches other measurements in the local universe, and is somewhat in tension with values obtained when the universe was young."
This investigation of supernova Hope began when Frye and her global team of scientists found three curious points of light in a JWST image of a distant, densely packed cluster of galaxies. Those points of light in the image were not visible when the Hubble Space Telescope imaged the same cluster, known as PLCK G165.7+67.0 or, more simply, G165, back in 2015. "It all started with one question by the team: 'What are those three dots that weren't there before? Could that be a supernova?'" Frye said.
The team noted a "high rate of star formation... more than 300 solar masses per year," according to NASA's statement: Dr. Frye: "Initial analyses confirmed that these dots corresponded to an exploding star, one with rare qualities. First, it's a Type Ia supernova, an explosion of a white dwarf star. This type of supernova is generally called a 'standard candle,' meaning that the supernova had a known intrinsic brightness. Second, it is gravitationally lensed. Gravitational lensing is important to this experiment. The lens, consisting of a cluster of galaxies that is situated between the supernova and us, bends the supernova's light into multiple images...
To achieve three images, the light traveled along three different paths. Since each path had a different length, and light traveled at the same speed, the supernova was imaged in this Webb observation at three different times during its explosion... Trifold supernova images are special: The time delays, supernova distance, and gravitational lensing properties yield a value for the Hubble constant... The team reports the value for the Hubble constant as 75.4 kilometers per second per megaparsec, plus 8.1 or minus 5.5... This is only the second measurement of the Hubble constant by this method, and the first time using a standard candle.
Their result? "The Hubble constant value matches other measurements in the local universe, and is somewhat in tension with values obtained when the universe was young."
Re:Those error bars are huge. (Score:5, Informative)
The premise of which is childish to say the least. The idea that all the money spent on JWST would just be laying around to be used for a natural disaster nearly thirty years in the future.
How weak.
Re: Those error bars are huge. (Score:1)
What if the universe is expanding at different rates all over?
Re: (Score:1)
Re: hubble did not believe universe is expanding. (Score:2)
Constant (Score:2)
Re: (Score:1)
Constant in space, not time. Even the most simple cosmological models currently considered don't think we live in a de Sitter universe.
The Friedmann equation is Hubble^2 = (constants) * energy density + Possible spatial curvature/a^2
Where Hubble = 1/a da/dt and a is the scale factor or "size" of the universe (or representative cell therein).
And if it's not constant in space (or has different rates of expansion in different directions) then we have to rethink the cosmological principles (homogeneity and isot
Another way to view it (Score:2)
Constant in space, not time. Even the most simple cosmological models currently considered don't think we live in a de Sitter universe.
The Friedmann equation is Hubble^2 = (constants) * energy density + Possible spatial curvature/a^2
Where Hubble = 1/a da/dt and a is the scale factor or "size" of the universe (or representative cell therein).
And if it's not constant in space (or has different rates of expansion in different directions) then we have to rethink the cosmological principles (homogeneity and isotropy on large scales).
As the universe expands, the energy density reduces, so the Hubble parameter goes down. Eventually at the universe becomes void of matter it will tend to a constant set by the cosmological constant (we think). But it has changed very much over the history of the universe.
The tension here is that if we take the current observed value and track it back to early times, the observed value doesn't quite match up with the values we'd get if we just took the earliest observations. There's a lot of possible reasons for this, but don't think that we haven't considered "it's not a constant" - we have. Extensively.
Another way to view it is to think in terms of construction.
Assume the universe is computable, that means it can be simulated using a computer program.
The program has to represent space in some way, and regardless of the implementation (or compression algorithm) space can be considered a large 3D array of points, possible positions in the universe.
If expansion is homogenous, then all of space is expanding all the time. Everywhere you look you see everything expanding away from you, like the surface of an ex
Re: (Score:2)
1) We already know it isn't necessary under the current model for it to be constant. The Inflationary Epoch is worth reading up on.
2) The issue isn't that it might be variable, the issue is we have two presumed reliable methods for measuring it, and we're getting two different answers whose margins of error do not overlap.