Dark matters by Adam Block

Posted by Michael Bakich
on Monday, June 08, 2015

We are happy to present another guest blog by astroimager Adam Block. Each of his blogs features a great image and something special about it. This one links Block with cutting-edge research into galaxy formation.

This gorgeous image of spiral galaxy NGC 4414 required 27 hours of exposures through the 32-inch Schulman Telescope at the Mount Lemmon SkyCenter. // Adam Block/Mount Lemmon SkyCenter/University of Arizona
We live in a universe in which we see only highlights. Most of the matter is cold, dark, and clumpy stuff that neither absorbs nor emits light. Its existence is inferred from gravitational influence by how it, like the stuff we are made of, warps space-time. Clumpy is the key. According to computer models that astronomers create, dark matter fragmented the early universe and promoted the formation of small (dwarf) galaxies. Larger galaxies, like our own, were built from the accretion and collision of smaller ones.

If true, we expect to see many more dwarf galaxies today than we do. Some astronomers, such as David Martinez-Delgado at the University of Arizona, investigate why we do not see as many as predicted today. It could be that dwarf galaxies were assimilated into larger galaxies at greater rates in the past or perhaps they are still around but difficult to see. So Martinez-Delgado and his team look at spiral galaxies in search of dwarf galaxies that may now be falling into larger ones. As they fall, they leave trails of stars that loop around large galaxies. As the stars orbit about they may eventually spread out to form even more diffuse shell-like structures.

These star streams can support explanatory theories that include cold dark matter, which ties in to the evolution of our universe. The accretion of dwarf galaxies may also trigger higher than expected star formation within the disks of large galaxies.

Over the last 10 years many examples have been found by taking very long exposures of relatively well known galaxies. Due to the amount of time necessary, this is a niche that amateur astronomers have helped fill to confirm star streams.

Here's the image all the fuss is about. It is a high-contrast negative image that reveals the shell around NGC 4414. // Adam Block/Mount Lemmon SkyCenter/University of Arizona
The Mount Lemmon SkyCenter, in collaboration with Martinez-Delgado’s group, has stepped up to help. The SkyCenter took long exposures of NGC 4414 to capture what could be a dispersed dwarf galaxy surrounding this beautiful spiral. There are many Hubble Space Telescope (HST) pictures of this well-known galaxy. However the galaxy’s halo extends well beyond the field view of many large telescopes such as HST. The image on this page, rendered as a color picture for the first time, is the star stream (shell) surrounding NGC 4414.

The shell of stars surrounding NGC 4414 is faint. It took 27 hours of exposures to capture this feeble glow. Hopefully, it’s time well spent and it will help solve big mysteries. The SkyCenter hopes you think the time was well spent to show you something virtually no one has seen before.

For more information about Martinez-Delgado’s research, click here.

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