M81 Galaxy - Infrared View of Stars

The Galaxy M81

This 3D model is built from an infrared image of the galaxy M81. It represents image brightness as elevation, translating intensity into a tactile and visual experience.

M81 is a classic example of a spiral galaxy that, from our perspective, is viewed obliquely at a 60 degree inclination.

What data went into this model?

This is an observation made in infrared light by NASA's Spitzer Space Telescope at a wavelength of 3.6 microns. In this part of the spectrum we can see through the dark dust lanes that obscure visible light images, providing what is effectively a census of where the stars reside in the galaxy.

You can learn more about the original image on the AstroPix.

What does this model show us?

In this 3D print we can see that the density of stars in the center of the galaxy is dramatically higher than in its outer disk. This is less obvious in images which can be heavily overexposed, hiding just how bright this region can be.

The two arcing ramps along either side show the two primary spiral arms where there is a slightly higher density of stars.

Note that this model is only displays the brightness in this image, not the three-dimensional shape of the galaxy (which would be essentially a thin, flat disk with a slight bulge at its center).

Data Processing

The print is not an exact representation of the original infrared data; several steps were take to make it work more effectively as a 3D print.

First, the foreground stars needed to be removed so the print would not be covered in sharp spikes that would obscure the view of the more distant galaxy.

Next, the image was adjusted to scale down the height of the central spike of starlight relative to the outer disk. In math terms, the image was processed with an inverse hyperbolic sine (asinh) that keeps the fainter features in linear proportions while reducing the brightest features logarithmically. Without this step, the central peak would be unprintably tall (and sharp)!

The final mesh was generated in Blender, using the image data to displace a flat mesh. At this stage the mesh was further smoothed to reduce sharp features.