Starship Asterisk*

orin stepanek wrote:
No massive black hole; but this galaxy has a massive bar!

Sandstone wrote:Clicking through the links embedded in the caption, came to the Hubblesite.org website, where this image was posted Jan 10, 2005.

It's an interesting reflection to see how far we've come with computing power and digital imagery since then, as the "full resolution" version (the same one posted on APOD when you click the main image, 6637 x 3787 pixels), came with this warning (in 2005):

"FILE DOWNLOAD WARNING: You are attempting to access an image with an extremely high resolution. Please read on before downloading any of these images or return to other image format options."

then goes on to say

"If you still want to use this format, we strongly recommend that you download our "high resolution images" rather than our "full resolution images." The "high resolution images" provide a more manageable file size for most computers. Very few computers will be able to handle the "full resolution images..."

They do offer, among other alternatives, a "Large" format version, 800 x 456 pixels, and a "Small" format at 200 x 200 pixels.

Have things really changed that much in 7 years?

moonstruck wrote:Another amazing Hubble image. Does anyone know how they aim the Hubble in all different directions to zero in on an image? Is someone on earth looking at a monitor and say ahh there's something "click"? Or does it automatically know how to find things by the light the images are transmitting. Or what? :?

Chris Peterson wrote:

moonstruck wrote:Another amazing Hubble image. Does anyone know how they aim the Hubble in all different directions to zero in on an image? Is someone on earth looking at a monitor and say ahh there's something "click"? Or does it automatically know how to find things by the light the images are transmitting. Or what?

The HST does nothing on its own. All the available imaging time is assigned to researchers via a complex process, and those researchers choose what they want to image. The HST is aimed at its chosen target using reaction wheels and magnetic torquers.

There is no realtime display on the ground of what the telescope is imaging. After an image is collected, the data is downloaded and can be viewed in its raw form, but isn't really useful until a complex calibration process is followed to remove systematic artifacts.

http://www.stsci.edu/hst/proposing/documents/primer/Ch_2_Systemoverview3.html wrote:
<<HST is in a relatively low orbit (~600 km above Earth), which imposes a number of constraints upon its observations. As seen from HST, most targets are occulted by the Earth for varying lengths of time during each 96-minute orbit. Targets lying in the orbital plane are occulted for the longest interval—about 44 minutes per orbit. These orbital occultations, analogous to the diurnal cycle for ground-based observing, impose the most serious constraint on HST observations. (Note that in practice the amount of available exposure time in an orbit is further limited by Earth-limb avoidance limits, the time required for guide star acquisitions or re-acquisitions, and instrument overheads.) The length of target occultation decreases with increasing angle from the spacecraft orbital plane. Targets lying within 24 degrees of the orbital poles are not geometrically occulted at any time during the HST orbit. This gives rise to so-called Continuous Viewing Zones (CVZs). The actual size of these zones is less than 24 degrees due to the fact that HST cannot observe close to the Earth limb. Since the orbital poles lie 28.5 degrees from the celestial poles, any target located in two declination bands near +/– 61.5 degrees may be in the CVZ at some time during the 56-day HST orbital precession cycle. Some regions in these declination bands can be unusable during the part of the year when the sun is too close to the region. The number and duration of CVZ passages depend on the telescope orbit and target position, and may differ significantly from previous cycles.>>

JuanAustin wrote:is there a correlation between the number of times a bar makes a rotation with number of years? i'm assuming the trailing arms would be longer and the spiral would be tighter?

JuanAustin wrote:
is there a correlation between the number of times a bar makes a rotation with number of years? i'm assuming the trailing arms would be longer and the spiral would be tighter?

http://en.wikipedia.org/wiki/Spiral_galaxies wrote:
<<In April 2011 a presentation to the Royal Astronomical Society's April 2011 National Astronomy Meeting in Llandudno, Wales by postgraduate student Robert Grand, suggested that spiral arms do not rotate rigidly at a constant angular velocity about the galactic centre. This contradicts a 50 year old theory called Spiral Density Wave Theory (SDWT), which states that the spiral arm pattern we see is actually a wave pattern, that rotates independently of star and inter-stellar matter that follow the standard rotation curve of the galaxy. Stars that move faster than the arms can overtake them and move through them. Consequently, stars outside this radius move slower than the arm and fall behind. Rather than a long-lived rigidly rotating wave pattern found in SDWT, Grand's simulations suggested that the arms rotate with a pattern speed that decreases with radius, and that they are transient features, with some arms breaking up and new ones being formed over periods of 80 to 100 million years. Instead of stars rotating independently of the arm pattern, they co-rotate at every radius, as the arm pattern speed traces very well the rotation curve of matter. The destruction of the arms is due to a declining pattern speed, which means that the arms begin to wind up and so break to avoid the well-known Wind-Up problem. This pattern of arm formation and destruction has not been observed in real galaxies, mainly because this pattern would take tens of millions of years to observe from start to finish. As observers, we can only observe what is a relative "snapshot" of a galaxy's evolution, and since there are always new arms forming as older ones die, there is always a spiral pattern present. Therefore, a simple glance at a galaxy will not yield evidence either way. A real observational contribution will come from the Gaia satellite, due to be launched in the coming years.>>

neufer wrote:

orin stepanek wrote:
No massive black hole; but this galaxy has a massive bar!

No KNOWN massive black hole.

The strong central vortex may be indicative of a massive central black hole surrounded by so much local angular momentum that there is nothing for it to eat and thereby give itself away by "burping."

Ann wrote:I thought that the fact that the arms "curve back" so strongly and barely "leave the bar" also suggests that there is a lot of mass in the center of NGC 1300.

ricardelico wrote:
Is a galaxy barred because of another galaxie's gravitational disruption of its original spiral form?

ricardelico wrote:Is a galaxy barred because of another galaxie's gravitational disruption of its original spiral form? Thank you for APoD.

Chris Peterson wrote:

ricardelico wrote:
Is a galaxy barred because of another galaxie's gravitational disruption of its original spiral form?

Probably not. It's more likely that the bar structure is a density wave system, similar to the spiral arms, and resulting from some sort of orbital resonance. Bars may exist in most or all spiral galaxies earlier in their evolution, eventually decaying away and leaving an unbarred spiral.

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

[b][color=#0000FF]Under the de Vaucouleurs classification system, SB-galaxies are one of three types of spiral galaxy[/color][/b]

---

<<Edwin Hubble classified these types of spiral galaxies as "SB" (spiral, barred) in his Hubble sequence, and arranged them into three sub-categories based on how open the arms of the spiral are. SBa types feature tightly bound arms, while SBc types are at the other extreme and have loosely bound arms. SBb-type galaxies lie in between. A fourth type, SBm, was subsequently created to describe somewhat irregular barred spirals, such as the Magellanic Cloud galaxies, which were once classified as irregular galaxies, but have since been found to contain barred spiral structures. Among other types in Hubble's classifications for the galaxies are: spiral galaxy, elliptical galaxy and irregular galaxy.

In 2005, observations by the Spitzer Space Telescope backed up previously collected evidence that suggested the Milky Way is a barred spiral galaxy. Observations by radio telescopes had for years suggested the Milky Way is barred, but Spitzer's vision in the infrared region of the spectrum has provided a more definite calculation.

Barred spiral galaxies are apparently predominant, with surveys showing that up to two-thirds of all spiral galaxies contain a bar. The current hypothesis is that the bar structure acts as a type of stellar nursery, fueling star birth at their centers. The bar is thought to act as a mechanism that channels gas inwards from the spiral arms through orbital resonance, in effect funneling the flow to create new stars. This process is also thought to explain why many barred spiral galaxies have active galactic nuclei, such as that seen in the Southern Pinwheel Galaxy.

The creation of the bar is generally thought to be the result of a density wave radiating from the center of the galaxy whose effects reshape the orbits of the inner stars. This effect builds over time to stars orbiting further out, which creates a self-perpetuating bar structure.

Bars are thought to be a temporary phenomenon in the life of spiral galaxies, the bar structure decaying over time, transforming the galaxy from a barred spiral to a "regular" spiral pattern. Past a certain size the accumulated mass of the bar compromises the stability of the overall bar structure. Barred spiral galaxies with high mass accumulated in their center tend to have short, stubby bars. Since so many spiral galaxies have a bar structure, it is likely that it is a recurring phenomenon in spiral galaxy development. The oscillating evolutionary cycle from spiral galaxy to barred spiral galaxy is thought to take on the average about two billion years.

Recent studies have confirmed the idea that bars are a sign of galaxies reaching full maturity as the "formative years" end. A team led by Kartik Sheth of the Spitzer Science Center at the California Institute of Technology in Pasadena discovered that only 20 percent of the spiral galaxies in the distant past possessed bars, compared with nearly 70 percent of their modern counterparts.>>

StarCuriousAero wrote:Has there been any effort to correlate a galaxy's location/trajectory (with respect to us and/or big bang origin) with its type/classification (and hence its "age" if you can call it that)?

Is there a concentration of "young" barred-galaxies near our own? Or are different types of galaxies relatively evenly distributed?