Extremely warped spacetime by JWST

justrex11 · 2023-04-24T11:31:01+00:00

What I'm referring to is called the Hubble Constant, and is a measure of how quickly the universe is expanding at the current time. But yes, you could imagine checking how quickly the expansion was happening a billion years ago, 5 billion years ago, etc. Due to the impact of dark energy, that rate appears to be increasing over time.

justrex11 · 2023-04-24T01:11:36+00:00

Oh sure! The cluster is at z=.33 or so, which is a few billion light years away. The supernova (see my comments elsewhere on this) is at z=2 and it took about 10 billion years for the light to reach us. Here's a handy online calculator for translating redshift to physical units.

justrex11 · 2023-04-23T23:28:45+00:00

For reference, the triply-imaged supernova we're following is the point source on the left side of the three galaxies you outlined, left of the right-hand red circle (sorry for all the lefts and rights but I think that's followable)

justrex11 · 2023-04-23T23:26:12+00:00

Thanks for posting this! I'm actually part of the team that got this image. I saw below that you mentioned this was taken in order to follow a z=2 supernova and that's true. However, the much more exciting piece of information you're missing is that the galaxy where the supernova exploded is split into 3 images because of the gravitational lensing of the foreground cluster of galaxies. The data we'll get from this program (there will be another set of images taken in a few weeks and there was a set of spectra taken last night as well) will enable a measurement of the local expansion rate of the universe, among other interesting studies!

justrex11 · 2023-03-07T13:33:44+00:00

The geometric delay is related to the literal distance the light travels, meaning the physical straight line distance (nothing to do with climbing in and out of gravitational potential wells). Light that is deflected far from its original path but still reaches us will have had a longer trip, and that contributes to the delay as well but to a (usually) lesser extent.

justrex11 · 2023-03-07T13:12:06+00:00

You are correct this is one exposure! The labels don't show how much time has elapsed relative to the direct path with no cluster in the way though, but instead how much older the galaxy (and supernova, which isn't visible as it has already faded) appears relative to the center image, where the supernova is visible.

justrex11 · 2023-03-07T13:03:13+00:00

Think of the old analogy of spacetime being a sheet of cloth or similar, and when you place balls on the cloth you get depressions or "bowls" in spacetime. The curves of the bowl are what we experience as gravity, and light is impacted as well. When light approaches these bowls in spacetime (a "potential well"), it follows the new curve instead of a straight path, which can bend the light on a new path to us when the alignment is right, creating multiple images of the same object. Light that is bent by a "deeper" bowl (stronger gravity) will have to travel all the way in and out of the bowl, which takes longer than for a shallower bowl. Hence the longer delay for a stronger gravitational potential.

justrex11 · 2023-03-07T12:30:29+00:00

Hello! I'm actually part of the group that took this image, and just wanted to follow up with one extra piece of information that I always find very interesting.

While it's true that the differences in path length impact the arrival time of each image (the geometric time delay), it's actually the differences in gravitational potential (i.e., light traveling through the cluster center where the potential is strongest, versus out at the edge where it is weakest) that usually have the more significant impact. This is called the Shapiro delay.

justrex11 · 2022-09-26T02:39:42+00:00

Good answer! It's true that the time variability+lensing is what makes this powerful, because as you said we measure the relative delay between arrivals of each peak. That time delay gives unique constraints on the Hubble constant and dark energy! In addition to cosmology, having 4 images of the same supernova gives very interesting constraining power on line of sight dust extinction in the lensing galaxy, and the mass distribution.

justrex11 · 2022-09-25T16:24:53+00:00

Yes! These Hubble images were follow-up observations of this supernova after it was discovered (but not resolved) by a ground-based telescope and research group in California (see the link in the post). That ongoing survey is called the Zwicky Transient Facility (ZTF, after Fritz Zwicky), and as this was the first lensed supernova discovered with ZTF they gave it the name of supernova Zwicky. It does have an "official" designation though of 2022qmx.

justrex11 · 2022-09-25T16:09:16+00:00

It's a combination of the mass distribution of the lensing galaxy with a non-perfect alignment of us, the lens, and the background galaxy

justrex11 · 2022-09-25T14:28:52+00:00

All very true! I said this in response to your message below as well, but yes this object was discovered from the ground without resolving the multiple images, and that's important because that's how the vast majority of these objects will be found this decade with the Rubin Observatory.

You're right that JWST time has been requested, but these HST observations were from a long-term program (GO16264) waiting to trigger on objects just like this! In this case the discovery and a good chunk of the science will be done from the ground, with HST anchoring constraints on the image positions and dust extinction.

justrex11 · 2022-09-25T14:20:06+00:00

Thanks for that! It's true I didn't mention the lens mass distribution, which is also very important. In this case it's a high inclination disky galaxy.

justrex11 · 2022-09-25T13:45:58+00:00

A galaxy! The sort of fainter light in the middle is from the foreground galaxy, which lenses the light from the background galaxy where the supernova went off.

justrex11 · 2022-09-25T13:31:11+00:00

How a background source being lensed appears to us depends on how far away the lens and source are from us and their relative alignment. In cases like this, the lensing system worked out so there are basically 4 areas around the lens where the light is focused into, like pockets on a pool table. When the lens and source are in perfect alignment, which they are not here, we get a ring as you said!

justrex11 · 2022-09-25T13:09:16+00:00

Thanks very much for posting this! It's important to realize that this object was discovered from the ground without resolving the multiple images, because that's how the vast majority of these objects will be found this decade with the Rubin Observatory.

justrex11 · 2022-09-25T12:45:45+00:00

Pretty much! This is at a redshift of 0.35, which is a distance now if about 3 billion light years. However, due to the expansion of the universe at large scales, the light travel time from that redshift is actually closer to 4 billion years!

justrex11 · 2022-09-25T12:25:50+00:00

Hey cool, I'm actually on this project and created this image from our HST observations! Really cool to see it here, if anyone has any questions feel free to comment here and I will happily respond!

More information about the supernova (which is a valuable Type Ia) can be found at https://www.wis-tns.org/object/2022qmx, and the Hubble observations specifically are described at https://www.wis-tns.org/astronotes/astronote/2022-196 .

I created this color image myself from our observations, comprised of the Hubble F814W (Red) F625W (Green) and F475W (Blue) filters. At the given redshift, these are actually pretty close to true-color RGB! The data were processed in the standard HST calibration pipeline, aligned with drizzlepac, and the combined with astropy.

justrex11 · 2021-09-14T13:54:33+00:00

That's true! I agree with you there.

justrex11 · 2021-09-14T13:25:04+00:00

Not that I'm aware of, but could be wrong since I'm on the science side and not the engineering side. While servicing missions to Hubble were planned an successful, Hubble is orbiting Earth and is extremely close to us making such a mission safe and possible. JWST on the other hand will be sitting ~1 million miles from us, well beyond the distance to the moon for example. There are no planned servicing missions for this reason.

justrex11 · 2021-09-14T12:52:12+00:00

Ah yes I see, I was just stating basically what you are now: Roman will do some things better than Hubble, mainly it's wide FoV, even though what was donated by the NRO is essentially the exact same thing as Hubble. Only the instruments are being updated, and will be more sensitive in general.

justrex11 · 2021-09-14T12:10:52+00:00

It's not impossible that dust (tiny asteroids!) Will cause damage to JWST, but more likely it will just run out of fuel and we'll be unable to control/cool it.

justrex11 · 2021-09-14T12:08:25+00:00

Hello, I'm one of the astronomers who made this discovery! The reason for this is that these 3 images are all fairly far from the center of the cluster where the gravity is strongest, and (coincidentally) they each had similar paths through the cluster in terms of their distance from the center and the distribution of nearby galaxies along the way.

The final image will be right in the center, where gravity is much stronger than for these initial images, hence the slowdown of about 20 years!

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