APOD: Rumors of a Dark Universe (2019 Aug 04)

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APOD: Rumors of a Dark Universe (2019 Aug 04)

Post by APOD Robot » Sun Aug 04, 2019 4:07 am

Image Rumors of a Dark Universe

Explanation: Twenty-one years ago results were first presented indicating that most of the energy in our universe is not in stars or galaxies but is tied to space itself. In the language of cosmologists, a large cosmological constant -- dark energy -- was directly implied by new distant supernova observations. Suggestions of a cosmological constant were not new -- they have existed since the advent of modern relativistic cosmology. Such claims were not usually popular with astronomers, though, because dark energy was so unlike known universe components, because dark energy's abundance appeared limited by other observations, and because less-strange cosmologies without a signficant amount of dark energy had previously done well in explaining the data. What was exceptional here was the seemingly direct and reliable method of the observations and the good reputations of the scientists conducting the investigations. Over the two decades, independent teams of astronomers have continued to accumulate data that appears to confirm the existence of dark energy and the unsettling result of a presently accelerating universe. In 2011, the team leaders were awarded the Nobel Prize in Physics for their work. The featured picture of a supernova that occurred in 1994 on the outskirts of a spiral galaxy was taken by one of these collaborations.

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Re: APOD: Rumors of a Dark Universe (2019 Aug 04)

Post by Boomer12k » Sun Aug 04, 2019 8:03 am

That has to be the DUSTIEST Galaxy there is... they got DUST BUNNIES there... you thought you had it bad.... :lol2:

It also show that there can be stars where we don't necessary think we would see stars....

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Re: APOD: Rumors of a Dark Universe (2019 Aug 04)

Post by De58te » Sun Aug 04, 2019 8:22 am

The statement that it was noteworthy that the scientists conducting the investigation had good reputations got me to thinking. Remember the days, long ago, when scientists conducting investigations had bad reputations? Ahh, those were the bad old days.

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Re: APOD: Rumors of a Dark Universe (2019 Aug 04)

Post by Ann » Sun Aug 04, 2019 9:16 am

Boomer12k wrote:
Sun Aug 04, 2019 8:03 am
That has to be the DUSTIEST Galaxy there is... they got DUST BUNNIES there... you thought you had it bad.... :lol2:

It also show that there can be stars where we don't necessary think we would see stars....

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Actually NGC 4526 is not very dusty at all. It is a lenticular galaxy which, like all lenticular galaxies, is generally poor in gas and dust, but NGC 4526 has a disk of gas and dust near its center.

The central part of lenticular galaxy NGC 4526 with supernova 1994D.
High-Z Supernova Search Team, HST, NASA
Wide-angle view of NGC 4526.
Note that the star to the right of the dust disk is not the supernova.
Image Credit: ESA/Hubble & NASA, Judy Schmidt



























The position of the supernova would have been to the upper left of the conspicuous star next to the dust disk in the picture at right.

Note that the supernova was not found on the outskirts of NGC 4526, as the APOD caption said, but merely on the outskirts of the central dust disk.
Spacetelescope wrote:

NGC 4526 is part of the Virgo cluster of galaxies. A quarter of the galaxies in this cluster seem to have rapidly rotating discs of gas at their centers. The most spectacular of these is this galaxy, NGC 4526, whose spinning disc of gas, dust, and stars reaches out uniquely far from its heart, spanning some 7 percent of the galaxy’s entire radius.

This disc is moving incredibly fast, spinning at more than 250 kilometers per second. The dynamics of this quickly whirling region were actually used to infer the mass of NGC 4526’s central black hole — a technique that had not been used before to constrain a galaxy’s central black hole.
The black hole at the center of NGC 4526 has a mass of 450 million Suns, according to Spacetelescope.

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Re: APOD: Rumors of a Dark Universe (2019 Aug 04)

Post by JohnD » Sun Aug 04, 2019 10:35 am

I presume that the supernova is the star at 7 o'clock in the APOD?
"In the outskirts of a galaxy"? That nova is half a galactic radius outside the rim! It's not in the outskirts, it's way, way beyond, so far as to question its association.
Various online authorities give their distances from us as 55 and 50 million light years. Can't find a diameter for that galaxy, but they are quoted in thousands on LYs, and this star is 5 MIllion LY nearer to us? Is it really part of NGC4526?
Could it be an intergalactic, 'rogue' star, ejected from another galaxy, as suggested by Ryan Foley? See: https://academic.oup.com/mnras/article/ ... b3af63f3d9

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Re: APOD: Rumors of a Dark Universe (2019 Aug 04)

Post by orin stepanek » Sun Aug 04, 2019 11:47 am

"And the light shines in the darkness; and the darkness grabs it not," Kind of the way my brain works some days! :lol2: Maybe light can go faster through dark energy? :shock:
Orin

Smile today; tomorrow's another day!

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Re: APOD: Rumors of a Dark Universe (2019 Aug 04)

Post by Ann » Sun Aug 04, 2019 12:01 pm

Wide-angle view of lenticular galaxy NGC 4526.
Note that the conspicuous star to the right of the dusty disk is not the supernova.
Credit:ESA/Hubble & NASA, Acknowledgement: Judy Schmidt
I presume that the supernova is the star at 7 o'clock in the APOD?
JOhn
Yes.
"In the outskirts of a galaxy"? That nova is half a galactic radius outside the rim! It's not in the outskirts, it's way, way beyond, so far as to question its association.
Like you said, the supernova is not not on the outskirts of NGC 4526, but that's because it was located about halfway between the core and the outer diffuse edge of the galaxy. The dusty disk in the APOD is just the small inner disk of the galaxy. Look at the picture at left!
Various online authorities give their distances from us as 55 and 50 million light years. Can't find a diameter for that galaxy, but they are quoted in thousands on LYs, and this star is 5 MIllion LY nearer to us?


Establishing exact distances of objects millions of light-years away is tricky. So an estimate of 50 to 55 million light-years for the galaxy and the supernova is good enough. But I'd say it is certain that the supernova and the galaxy are not 5 million light-years away from one another!
Is it really part of NGC4526?
Could it be an intergalactic, 'rogue' star, ejected from another galaxy, as suggested by Ryan Foley? See: https://academic.oup.com/mnras/article/ ... b3af63f3d9
Light curves of 22 Supernovae type Ia. Source: ned.ipac.caltech.edu
Is the supernova really a part of NGC 4526? Yes, absolutely!

The reasons why we can be so sure that Supernova 1994D really belonged to galaxy NGC 4526 are twofold. First, the supernova happened well inside this galaxy, about halfway between the center and the edge. Second, it was a type Ia supernova, and this type of supernovas have extremely distinctive light curves and well understood absolute luminosities. SN 1994D had just the sort of luminosity that could be expected from a supernova type Ia at the distance of NGC 4526.

Moreover, the fact that SN 1994D was a type Ia supernova means that it didn't receive a huge kick when it exploded, because SN type Ia don't function like that. The supernova remnants that can get a kick away from their birthplaces are core collapse supernovas, the ones that form neutron stars or black holes when they explode. Core collapse supernovas can explode asymmetrically and send their neutron stars or black holes flying.

So Supernova 1994 was not an interstellar visitor, and itself and its progenitor always belonged to galaxy NGC 4526.

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Re: APOD: Rumors of a Dark Universe (2019 Aug 04)

Post by Chris Peterson » Sun Aug 04, 2019 1:16 pm

Boomer12k wrote:
Sun Aug 04, 2019 8:03 am
That has to be the DUSTIEST Galaxy there is... they got DUST BUNNIES there... you thought you had it bad.... :lol2:

It also show that there can be stars where we don't necessary think we would see stars...
Only if we limit what we mean by "see" to one specific dataset. We have other ways of looking at galaxies like this where stars can't hide behind dust.
Chris

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Re: APOD: Rumors of a Dark Universe (2019 Aug 04)

Post by Chris Peterson » Sun Aug 04, 2019 1:17 pm

De58te wrote:
Sun Aug 04, 2019 8:22 am
The statement that it was noteworthy that the scientists conducting the investigation had good reputations got me to thinking. Remember the days, long ago, when scientists conducting investigations had bad reputations? Ahh, those were the bad old days.
Fortunately, a scientist (or anybody else, for that matter) need not have a bad reputation simply because they lack a good one!
Chris

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Re: APOD: Rumors of a Dark Universe (2019 Aug 04)

Post by Ann » Sun Aug 04, 2019 3:28 pm

Chris Peterson wrote:
Sun Aug 04, 2019 1:16 pm
Boomer12k wrote:
Sun Aug 04, 2019 8:03 am
That has to be the DUSTIEST Galaxy there is... they got DUST BUNNIES there... you thought you had it bad.... :lol2:

It also show that there can be stars where we don't necessary think we would see stars...
Only if we limit what we mean by "see" to one specific dataset. We have other ways of looking at galaxies like this where stars can't hide behind dust.
Right you are, Chris, but when it comes to NGC 4526 we can say for sure that it isn't very dusty. That is obvious when we compare its blue and far infrared magnitudes. Its blue (B) magnitude is 10.6, whereas its far infrared magnitude is 11.0.

This means that NGC 4526 is fainter in far infrared than in blue light, and far infrared light signals dust. Okay, the difference between far infrared and blue light in NGC 4526 isn't great, but still we are right to assume that NGC 4526 isn't very dusty. But its inner disk certainly is.

We may compare NGC 4526 with M64, the Black-Eye Galaxy, which is another galaxy that has a small and very dusty inner disk, and a large almost dust-free outer disk. M64 is almost equally bright in blue and far infrared light, meaning that it is comparatively dustier than NGC 4526.

The Andromeda Galaxy in near-ultraviolet, visible and near infrared by Hubble.
Andromeda in far infrared by Herschel.
















Our huge neighbour Andromeda, by contrast, is relatively dust-poor. M31 is 1.3 magnitudes fainter in far infrared than in blue light. And if you look at the pictures above, you can see how bright the inner bulge of Andromeda is in visible and near infrared light, but how comparatively faint the same region is in far infrared light. And as I said, far infrared light is primarily emitted by dust.

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Re: APOD: Rumors of a Dark Universe (2019 Aug 04)

Post by dlw » Sun Aug 04, 2019 5:21 pm

Perhaps I'm missing something but I wonder whether the statement "a supernova that occurred in 1994" might more properly be "a supernova that was observed in 1994." Apparently it "occurred" some 50 million years ago.

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Re: APOD: Rumors of a Dark Universe (2019 Aug 04)

Post by Chris Peterson » Sun Aug 04, 2019 5:27 pm

dlw wrote:
Sun Aug 04, 2019 5:21 pm
Perhaps I'm missing something but I wonder whether the statement "a supernova that occurred in 1994" might more properly be "a supernova that was observed in 1994." Apparently it "occurred" some 50 million years ago.
For all practical purposes, they are the same thing. There is almost never any reason to try and figure out when something "really" happened. When we're observing a process, like a supernova, t=0 is defined by the observation time.
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Re: APOD: Rumors of a Dark Universe (2019 Aug 04)

Post by ta152h0 » Sun Aug 04, 2019 6:39 pm

Is it possible the Universe existed before the Big Bang event at absolute 0 temperature and the Big Bang was just a fuse that was lit and the fire spread?
pass the ice cold one.
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Re: APOD: Rumors of a Dark Universe (2019 Aug 04)

Post by Chris Peterson » Sun Aug 04, 2019 7:41 pm

ta152h0 wrote:
Sun Aug 04, 2019 6:39 pm
Is it possible the Universe existed before the Big Bang event at absolute 0 temperature and the Big Bang was just a fuse that was lit and the fire spread?
pass the ice cold one.
By definition, the Universe began with the Big Bang. Whether there was "something" that existed "before" is an open question.
Chris

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Re: APOD: Rumors of a Dark Universe (2019 Aug 04)

Post by JohnD » Sun Aug 04, 2019 9:22 pm

Thank you, Ann, for your detailed response to my question on the place and origin of SN 1994D. It clearly is in that galaxy when I look at the Hubble pic and realise that the 'haze' around it is a cloud of stars! The relative dimensions of space always catch me out.

So it's probably not one of Ryan Foley's 'rogue stars' then! But is it a calcium-rich SN? Can you tell from the colour?
John

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Re: APOD: Rumors of a Dark Universe (2019 Aug 04)

Post by Boomer12k » Sun Aug 04, 2019 10:31 pm

Ann wrote:
Sun Aug 04, 2019 9:16 am
Boomer12k wrote:
Sun Aug 04, 2019 8:03 am
That has to be the DUSTIEST Galaxy there is... they got DUST BUNNIES there... you thought you had it bad.... :lol2:

It also show that there can be stars where we don't necessary think we would see stars....

:---[===] *
Actually NGC 4526 is not very dusty at all. It is a lenticular galaxy which, like all lenticular galaxies, is generally poor in gas and dust, but NGC 4526 has a disk of gas and dust near its center.

The central part of lenticular galaxy NGC 4526 with supernova 1994D.
High-Z Supernova Search Team, HST, NASA
Wide-angle view of NGC 4526.
Note that the star to the right of the dust disk is not the supernova.
Image Credit: ESA/Hubble & NASA, Judy Schmidt



























The position of the supernova would have been to the upper left of the conspicuous star next to the dust disk in the picture at right.

Note that the supernova was not found on the outskirts of NGC 4526, as the APOD caption said, but merely on the outskirts of the central dust disk.
Spacetelescope wrote:

NGC 4526 is part of the Virgo cluster of galaxies. A quarter of the galaxies in this cluster seem to have rapidly rotating discs of gas at their centers. The most spectacular of these is this galaxy, NGC 4526, whose spinning disc of gas, dust, and stars reaches out uniquely far from its heart, spanning some 7 percent of the galaxy’s entire radius.

This disc is moving incredibly fast, spinning at more than 250 kilometers per second. The dynamics of this quickly whirling region were actually used to infer the mass of NGC 4526’s central black hole — a technique that had not been used before to constrain a galaxy’s central black hole.
The black hole at the center of NGC 4526 has a mass of 450 million Suns, according to Spacetelescope.

Ann
YES.... thank you Ann...today I did a search and I now see it is actually a MUCH bigger lenticular galaxy... the picture is so zoomed in, you just don't see it...

Thanks....
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Re: APOD: Rumors of a Dark Universe (2019 Aug 04)

Post by neufer » Sun Aug 04, 2019 10:49 pm

Chris Peterson wrote:
Sun Aug 04, 2019 7:41 pm
ta152h0 wrote:
Sun Aug 04, 2019 6:39 pm

Is it possible the Universe existed before the Big Bang event at absolute 0 temperature
and the Big Bang was just a fuse that was lit and the fire spread?
By definition, the Universe began with the Big Bang.
Whether there was "something" that existed "before" is an open question.
By definition :?:

By observation, the Universe evolves over time and early on:
  • 1) It was extremely hot.
    2) It had an extremely low entropy.
    3) And it was much more symmetric.
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Re: APOD: Rumors of a Dark Universe (2019 Aug 04)

Post by Chris Peterson » Sun Aug 04, 2019 11:15 pm

neufer wrote:
Sun Aug 04, 2019 10:49 pm
Chris Peterson wrote:
Sun Aug 04, 2019 7:41 pm
ta152h0 wrote:
Sun Aug 04, 2019 6:39 pm

Is it possible the Universe existed before the Big Bang event at absolute 0 temperature
and the Big Bang was just a fuse that was lit and the fire spread?
By definition, the Universe began with the Big Bang.
Whether there was "something" that existed "before" is an open question.
By definition :?:
Yes, by definition. At least, for all of the variations of the Big Bang model, which are really the only ones worth investing much effort in.
Chris

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Re: APOD: Rumors of a Dark Universe (2019 Aug 04)

Post by Ann » Mon Aug 05, 2019 4:33 am

JohnD wrote:
Sun Aug 04, 2019 9:22 pm
Thank you, Ann, for your detailed response to my question on the place and origin of SN 1994D. It clearly is in that galaxy when I look at the Hubble pic and realise that the 'haze' around it is a cloud of stars! The relative dimensions of space always catch me out.

So it's probably not one of Ryan Foley's 'rogue stars' then! But is it a calcium-rich SN? Can you tell from the colour?
John
Thanks, John! No, I can't tell from the color if a supernova is calcium-rich or not, but I do know that unreddened supernovas type Ia are blue. Core-collapse supernovas are often yellowish, but I don't know if they are always the same color.

Blue supernova PTF 11kx, type Ia.
Yellowish supernova 1987A, type II.





















Just a quick reminder here: A supernova type Ia explodes when a white dwarf has accreted too much mass to support itself via "electron degeneracy pressure". Supernovas type Ia always arise from white dwarfs of an almost given mass, and they explode in almost the same way, although some are a little brighter than others. They leave no central remnant behind, no neutron star or black hole.

Supernovas type II (and other core-collapse supernovas) explode when a massive star has used up all available sources of fusion in its core and ended up with an iron core. No energy can be extracted by the star from iron, and that creates a fatal imbalance in the star that leads to a tremendous explosion. (I'll leave it to you to try to figure out exactly how that explosion happens.) Supernovas type II leave neutron stars (or, in rare cases, black holes) behind. Interestingly, no neutron star has been found in the Supernova 1987A remnant.

Interestingly, supernova PTF 11kx was calcium-rich!
Universe Today wrote:

The Keck observations showed the PTF 11kx post-supernova system to contain slow-moving clouds of gas and dust that couldn’t have come from the recent supernova event. Instead, the clouds — which registered high in calcium in the Lick spectrographic data — must have come from a previous nova event in which the white dwarf briefly ignited and blew off an outer layer of its atmosphere.


But I have no idea if calcium in a supernova remnant will give either the supernova or its remnant a specific color.

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