Starship Asterisk*

Chris Peterson wrote:

Tszabeau wrote:I was pondering the scale of this image using the spiked stars as reference markers which, helps me gain some perspective. I have always assumed that the artifact spikes appear around relatively nearby stars within the Milky Way however, I notice a few of the galaxy's also appear to have spikes. Are those galaxies being superimposed by nearby spiked-stars making them just to appear that way or is the exposure, simply, deep enough to cause nearer galaxies to appear spiked as shallower exposures make nearer stars to?
Yes, I know the spikes are photographic artifacts.

Spikes are not photographic artifacts, they are optical artifacts caused by diffraction off the secondary mirror supports. Every object in the image has spikes, but for dim extended objects they are below the noise floor. Some galaxies have bright enough cores that they produce visible spikes in this deep image. They are real- not the product of nearby stars superimposed on the galaxies.

Indigo_Sunrise wrote:do you have a link to the Hubble eXtreme Deep Field

jmcgericault wrote:Hypothetical question: Could we see our own Milky Way galaxy -- as it was all those billions of years ago -- in these Hubble Deep Field images? Or if Hubble pointed its mirror in the direction from which our galaxy originated...

Chris Peterson wrote:

Tszabeau wrote:Since the spikes are not photographic artifacts but diffractions of mirror supports, does it follow that each telescope has its' own signature spike? Can the spikes be compensated or countered out of an image with software or optical means, based on the known structure of the mirror supports, like atmospheric shimmering is compensated for in earth-bound scopes?

Every telescope produces a diffraction pattern that is determined by its aperture characteristics- diameter, shape, and the size and shape of any occluding elements. A four-vane spider produces four spikes; a three-vane spider produces six spikes (each vane produces a pair; in the case of four vanes, spikes overlap); an eight-element iris produces eight spikes; an unobstructed circular aperture produces rings.

In principle, you could use deconvolution to reduce the spikes. However, that sort of reverse filtering typically has no closed solution (filters destroy information), and anything you do to reduce the spikes is likely to lead to new artifacts. Best to leave them. Indeed, some people add them digitally, or put crosshairs across their otherwise unobstructed telescope aperture in order to create them optically. Go figure!

neufer wrote:

tomatoherd wrote: Galaxies DO NOT grow bigger with time due to the expansion of the universe.

Ann wrote:It is the same field, but the earlier picture was made without any ultraviolet filters. You can find the B, R and several I's (infrared filters) image here.

Ann

tomatoherd wrote:you are correct, I'm guessing: they do not relative to another "inside" observer. But they do absolutely, i presume, to an outside observer, as does everything if space/time is expanding. Of course the only outside observer is God et al.....

Chris Peterson wrote:

tomatoherd wrote:

neufer wrote:
Galaxies grow bigger with time from absorbing/assimilating more gas and other galaxies.

Galaxies DO NOT grow bigger with time due to the expansion of the universe.

you are correct, I'm guessing: they do not relative to another "inside" observer. But they do absolutely, i presume, to an outside observer, as does everything if space/time is expanding. Of course the only outside observer is God et al.....

No. The expansion of spacetime is not uniform. Gravity easily overpowers expansion. Regions with strong gravitational fields don't expand. That includes galaxies. Spacetime is expanding around them, not through them.

http://en.wikipedia.org/wiki/The_big_rip wrote:

[b][color=#FF0000][size=135]God et Al: Big Al is the costumed mascot of the University of Alabama Crimson Tide in Tuscaloosa, Alabama.[/size][/color][/b]

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<<The Big Rip is a cosmological hypothesis first published in 2003, about the ultimate fate of the universe, in which the matter of the universe, from stars and galaxies to atoms and subatomic particles, is progressively torn apart by the expansion of the universe at a certain time in the future. According to the hypothesis, the scale factor of the universe and with it all distances in the universe will become infinite at a finite time in the future. It is important to note that the possibility of sudden singularities and crunch or rip singularities at late times occur only for hypothetical matter with implausible physical properties.

The hypothesis relies crucially on the type of dark energy in the universe. The key value is the equation of state parameter w, the ratio between the dark energy pressure and its energy density. At w < −1, the universe will eventually be pulled apart. Such energy is called phantom energy, an extreme form of quintessence.

A universe dominated by phantom energy expands at an ever-increasing rate. However, this implies that the size of the observable universe is continually shrinking; the distance to the edge of the observable universe which is moving away at the speed of light from any point moves ever closer. When the size of the observable universe becomes smaller than any particular structure, no interaction by any of the fundamental forces (gravitational, electromagnetic, weak, or strong) can occur between the most remote parts of the structure. When these interactions become impossible, the structure is "ripped apart". The model implies that after a finite time there will be a final singularity, called the "Big Rip", in which all distances diverge to infinite values.

The authors of this hypothesis, led by Robert Caldwell of Dartmouth College, calculate the time from the present to the end of the universe as we know it for this form of energy to be



where w is defined above, H₀ is Hubble's constant and Ω_m is the present value of the density of all the matter in the universe.

In their paper, the authors consider an example with w = −1.5, H₀ = 70 km/s/Mpc and Ω_m = 0.3, in which case the end of the universe is approximately 22 billion years from the present. This is not considered a prediction, but a hypothetical example. The authors note that evidence indicates w to be very close to −1 in our universe, which makes w the dominating term in the equation. The closer that the quantity (1 + w) is to zero, the closer the denominator is to zero and the further the Big Rip is in the future. If w were exactly equal to −1, the Big Rip could not happen, regardless of the values of H₀ or Ω_m.

In their scenario for w = −1.5, the galaxies would first be separated from each other. About 60 million years before the end, gravity would be too weak to hold the Milky Way and other individual galaxies together. Approximately three months before the end, the Solar System (or systems similar to our own at this time, as the fate of the Solar System 7.5 billion years in the future is questionable) would be gravitationally unbound. In the last minutes, stars and planets would be torn apart, and an instant before the end, atoms would be destroyed.

According to the latest cosmological data available, the uncertainties are still too large to discriminate among the three cases w < −1, w = −1, and w > −1.>>

DavidACaruso wrote:Am I missing something, or do I see hundreds of fully formed and evolved galaxies in the image?

tomatoherd wrote:

neufer wrote:

tomatoherd wrote: Galaxies DO NOT grow bigger with time due to the expansion of the universe.

you are correct, I'm guessing: they do not relative to another "inside" observer. But they do absolutely, i presume, to an outside observer, as does everything if space/time is expanding. Of course the only outside observer is God et al.....

DavidACaruso wrote:
Am I missing something, or do I see hundreds of fully formed and evolved galaxies in the image?

DavidACaruso wrote:Am I missing something, or do I see hundreds of fully formed and evolved galaxies in the image? Wouldn't simple common sense suggest that entire galaxies would take more than a few hundred million years to evolve to present forms?

NGC3314 wrote:

Krell1956 wrote:I would like to know more detail about the UV data and what it's adding to the Ultra Deep Field image. The APOD post says the UV data helped study star formation in galaxies 5 to 10 billion LY away. I haven't done the math on it, but I would think that even energetic gamma rays associated with star formation (if they ARE associated with star formation- doesn't seem energetic enough) would have red shifted to longer wavelengths than UV. Is there something I'm not reading right? Energetic black holes and star formation....?

The hallmark of star-forming regions (as long as they're not too dust-enshrouded) is intense radiation in the emitted UV part of the spectrum, so strongly that images are more and more sensitive to the level of star formation at shorter UV wavelengths until one reaches the Lyman limit where radiation has enough energy to ionize hydrogen (912 Angstroms, 91.2 nm, 13.6 eV photon energy). So UV data improve our census of cosmic star formation up to redshifts where the filter samples the "missing" radiation absorbed by gas in each galaxy. The new data use several near-UV filters down to 2250 A wavelength, so they show star formation to a redshift (2250-912)/912=1.46 (with a soft cutoff because of the width of the filter transmission). That would be a lookback time of about 9 Gyr.

To show how sensitive the UV is to recent star formation, this plot compares the spectra of bursts of star formation at billion-year intervals (top to bottom). The intensity scale is logarithmic, stressing how fast the population of stars both fades and reddens with time. (Taken from this class page)



One reason these data were taken now is that the sensitivity of the UV instruments on Hubble is declining noticeably year to year (which pretty much all UV detectors do in space, due to damage from particle impacts and accumulating contaminants if anything else in the system outgases), so for the last couple of years Hubble has been scheduled under a "UV Initiative", giving extra weight to UV observations while they're still easy.

DavidLeodis wrote:
The "Big Bang" link in the explanation brought up the APOD of March 23 2006 ('Inflating the Universe'). I was amused in the explanation to that APOD to read "Schematically, this diagram traces the 13.7 billion year (plus a trillionth of a second ...) history of the Universe". That trillionth of a second was clearly a monumental moment in that history!

http://en.wikipedia.org/wiki/Rubik%27s_Cube#Permutations wrote:
<<The original (3×3×3) Rubik's Cube has approximately 43 quintillion possible arrangements. The puzzle is often advertised as having only "billions" of positions, as the larger numbers are unfamiliar to many.>>