X-ray: NASA/CXC/SAO; UV: NASA/JPL-Caltech; Optical: NASA/STScI; IR: NASA/JPL-Caltech Earlier this year, NASA released this stunning new image of the Whirlpool Galaxy.
But don't be fooled by its beauty — this image has been manipulated by scientists to look different than how the galaxy actually appears in reality. But for good reason.
This image of the Whirlpool galaxy is a combination of four pictures — one taken by each of these NASA space telescopes:
Astronomers look at the sky with different instruments because in the grand scheme of things, the light that human eyes detect is only a small amount of the radiation out there, so they use these instruments to pick up the rest.
And the more they can see of the cosmos, the more they learn and understand about how it works.
To give you a better picture of how this works, we've broken down the image above into its components to describe how each one helps astronomers.
The full spectrum
Humans see only a small part of what scientists call the electromagnetic spectrum. This spectrum encompasses all forms of radiation — energy that moves through space. And the term "visible light" refers to the different colors that humans see every day:
Johannes Ahlmann/Flickr The electromagnetic spectrum. The thin part in the middle is the range of wavelengths our eyes perceive as color.
Each picture below is not what you would actually see if you were looking through a powerful telescope.
In order to study objects in different wavelengths, astronomers convert the non-visible parts of the spectrum into colors like purple, blue, and red. The color of the four pictures below reflect their energy levels — so from highest energy to lowest the photos start with X-rays in purple, ultra-violet in blue, visible light in green, and finally infrared in red.
Similar to how X-rays penetrate human skin, enabling doctors to see our bones, the Chandra X-ray Observatory can see parts of the Whirlpool Galaxy that astronomers could not see through a basic light-based telescope.
What Chandra saw when it turned its sights on the Whirlpool Galaxy was very different than the composite picture up top:
NASA/Chandra When astronomers look at X-ray images like the one above, they focus on the points that shine brightest. In this case, the bright, white dots represent sources of high-energy X-rays such as the hot gas either left-over after a star explodes or ejected from a supermassive black hole. The purple shows hot gas that is also emitting x-rays, but at lower temperatures than the bright white regions.
If you look at the center of this galaxy, you'll see a ton of high-energy X-rays. That's because the core of the Whirlpool galaxy is active, meaning the supermassive black hole at the center is sucking up the stars around it.
The gas and dust is being accelerated to tremendously high speeds and temperatures due to the black hole's immense gravity, and the hotter the it gets, the higher-energy radiation it emits.
Where baby stars are born
One of the ways astronomers can help determine the age of a galaxy is to look at how many stellar nurseries it has. Spiral galaxies, like the Whirlpool galaxy and the Milky Way, are middle-aged galaxies that produce on average between one and one hundred stars a year. (Younger galaxies can churn out hundreds of stars a year while older galaxies don't produce any new stars.)
Baby stars shine brightly in the ultra-violet part of the spectrum. NASA's Galaxy Evolution Explorer instrument sees in the ultra-violet and took the image below, which shows that this particular galaxy has a healthy amount of star formation pockets that show up as bright blue spots.
NASA GALEX Stars are born inside of dense, dusty clouds in space. As dust sticks together, it grows heavier, which attracts more dust. If a clump of dust grows dense enough, then the core will heat up and start generating nuclear fusion in its core. This hot gas emits light in the form of ultra-violet radiation, which is why astronomers study these wavelengths to figure out where stars are forming. Seeing in true color
The famous Hubble Space Telescope is one of the few space-based telescopes that sees what humans see. So, the details shown in the Hubble image below is what you would see if you could fly a spaceship to the Whirlpool galaxy about 25 million light years away, though not green in color.
It's tinted green because, in this case, NASA scientists are using a color scheme: The energy of light that Hubble sees is lower than what Chandra sees. Similarly, green light is lower in energy than purple, which is why this image is green and the Chandra image is purple. Without the color scheme, this picture would be black and white instead of black and green.
NASA Hubble Space Telescope One of Hubble's outstanding qualities is how well it can resolve distant objects. Just look at the level of detail in the image above compared to the more fuzzy ones taken by Chandra and GALEX.
What you see in this image that you can't see in any of the others is all of the dark patches that cut through the center of the galaxy's spiral arms.
While these regions show up as black in the Hubble image, notice that the exact same spots show up relatively bright in the infrared image taken by Spitzer (shown in red below). That's because dust is blocking visible light from reaching us, but the lower-energy infrared light penetrates the dust, which is why it shows up in the photo below, taken by the Spitzer Space Telescope.
A Dusty Place In Space
NASA's Spitzer Space Telescope specializes in a low-energy regime called the infrared. The photo below was taken by Spitzer:
NASA Spitzer Space Telescope Infrared light illuminates the dust within galaxies. Galaxies often contain lots of dust, which is why this image looks more complete and totally different from the ones taken by Chandra and GALEX.
All of the detail you see is dust that is cooler than the blazing-hot, black-hole kibble at the galaxy's center or in stellar nurseries. Astronomers use infrared telescopes like Spitzer to study low-temperature objects like dust and Jupiter-sized exoplanets.
In fact, one of Spitzer's most important discoveries was in 2005 when it became the first telescope to observe an exoplanet directly. (Before that, astronomers had found exoplanets by their gravitational pull on host stars that made the stars wobble, and so it was the wobble that they detected with very powerful telescopes.)
A beautiful false-color mashup
So, when you take the photos from Chandra, Spitzer, GALEX, and Hubble and put them all together you get the composite, false-color image below. Notice how the red-tinted veins in the spiral arms show up in this false-color picture though these areas show up black in the Hubble image:
X-ray: NASA/CXC/SAO; UV: NASA/JPL-Caltech; Optical: NASA/STScI; IR: NASA/JPL-Caltech After all of those false-colored pictures here's a photo of what this galaxy looks like for real, taken by an astrophotographer on Earth. We think it's the most beautiful one of them all:
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