Hubble Captures NGC 4102, an Unusual Spiral Galaxy Glowing in the Great Bear

High up in the sky above the Earth, NASA / ESA’s Hubble Space Telescope has been turned on NGC 4102 – a galaxy that isn’t one for loud and flashy displays. Perched 56 million light-years away in the constellation Ursa Major (Great Bear), this is a spiral galaxy that looks like its been caught mid-spin, with the music still playing, but paused.

Begin in the center of the galaxy, where a bright golden center gleams softly, a mass of gas being slowly dragged towards a supermassive black hole by an unseen force. That black hole is massive, weighing in at up to a billion Suns, yet it does not appear to be eating anything; rather, it appears to be feeding slowly. The gas becomes increasingly hotter as it is drawn towards the black hole, reaching millions of degrees at its hottest point before radiating down to the lovely soft light we see here. Unfortunately for us and the astronomers, thick curtains of gas wrap around the galaxy’s center so tightly that the majority of the X-rays produced by the hot gas never escape. Astronomers refer to this as a Compton-thick nucleus, which means that the galaxy’s heart preserves its secrets.

But step outside the central core, and you’ll notice a black gap that resembles a moat enclosing a medieval castle. Beyond that gloomy gap, however, a magnificent ring of sparkling sapphire and rose illuminates the scene. Little blue spots indicate the locations where gravity has coaxed young stars out of thin air. Pink clouds, on the other hand, reveal the nurseries where those stars were born, albeit only yesterday in cosmic time. If you look attentively, you’ll notice dust lanes winding around the ring in delicate brown ribbons, as if someone had painted a painting as the galaxy was whirling around.

One prominent arm sticks out, thick with light knots, as if it had changed its mind mid-pirouette. Hubble’s new Wide Field Camera 3 was able to pick out every last knot in incredibly fine detail. Compared to the 2014 portrait, which was taken with an older camera, the current shot is more like a painting – everything is nice and detailed, rather than a crude sketch.


Zooming out a little further reveals a faint halo of older stars that resembles the galaxy’s tranquil suburbs. The entire thing fits into a patch of sky that is visible with the naked eye if you hold your hand out at arm’s length and look at the tip of your finger. And yet, within that tiny patch of sky, there are hundreds of billions of stars, each spinning in its own orbit and contributing their own tiny bit of light to the overall picture.

By integrating Hubble’s visible-light images with Chandra’s X-ray maps, the scientists were able to gain a much more precise understanding of how the galaxy functions. And it indicates that the black hole is gently churning up the galaxy, forcing hot gas to rise up and cool before dropping back down and contributing to the formation of new stars. It is a cycle that occurs across millions of years, so the galaxy appears to be locked in place, yet in actuality it is constantly changing.


If you stand back and look at the spiral again, it appears almost tranquil. There are no flaming jets cutting across space, and no explosions tearing the galaxy apart. No, this galaxy moves at a slow pace and emits a pleasant, mellow light reminiscent of a hearth fire. It belongs to a class of galaxies known as LINERs (Little Blue, Very Energetic, Rocketing – or, in layman’s terms, galaxies with a black hole that sips rather than gulps), and because it is so quiet, it is ideal for astronomers to examine.