One of the perks of being a science journalist is being regularly wowed by the very best images from the world’s various space agencies. This week, Hubble was the darling, and the venerable space telescope has provided us these five absolutely beautiful images of stars, galaxies, and nebulae.
We’ll start with an elegant barred spiral galaxy about 130 million light-years from Earth, called NGC 5728. This image was taken in the optical and infrared bands, which provide a striking composition by themselves. What the image only hints at, however, is that NGC 5728 is a “monumentally energetic” place called a Seyfert galaxy. The brilliant glare in the center is what gives it away. These extremely high-energy galaxies are powered by their active cores, known as active galactic nuclei (AGNs).
Some AGNs emit so much radiation that they can blind the telescopes looking at them, but confining our observations to visible and IR light means that we can look straight into the center of this galaxy’s reactive core. To capture the portrait, Hubble used its Wide Field Camera (WFC), which is sensitive in these bands. Better still, the image is available from the ESA in sizes that make excellent wallpaper.
Next up is a glorious nebula surrounding a stellar nursery named NGC 346, which lies at the center of the Small Magellanic Cloud. The star-forming region is surrounded by a dramatic structure of columns and filaments. Outflows and explosions from the hot young stars are buffeting the clouds of the nebula, eroding the denser regions and leaving smokelike trails in their wake.
The sinuous ridge of dust that encircles the region stands out like an artist’s flourish. Hubble saw this structure in a highly detailed silhouette against the (very pink) background glow of the region. As new stars are born, more of the dust will be cleared away, revealing yet more star-forming regions within the cluster.
Elsewhere in the sky, the globular cluster NGC 6717 lies within the constellation Sagittarius, near the center of the Milky Way. Backscatter from the glow of the galactic center creates a luminous veil of dust around these tightly grouped stars. This obscuring effect is called “extinction.” Extinction makes it a challenge to observe this and other similar globular clusters, so astronomers used both the WFC and Hubble’s Advanced Camera for Surveys to create this image.
Foreground stars from closer to home can be seen in the center of the image. They are surrounded by “criss-cross diffraction spikes” resulting from interactions with Hubble’s secondary mirror.
Where NGC 6717 has extinction, observers of Palomar 6 must contend with reddening: a phenomenon where interposing gas and dust absorb some frequencies of starlight, changing what we see. Palomar 6 is another globular cluster close to the center of the galaxy. It is formally named ESO 520-21, and lies within the constellation Ophiuchus.
The constellation represents Asclepius, the Greek god of medicine, who is depicted grasping a snake. Ophiuchus was one of the original 48 constellations described by Ptolemy circa the second century. All 48 are among the 88 constellations currently recognized by the International Astronomical Union.
And finally, I present to you the blazing halo of color that is AG Carinae. This image is a composite of prior observations, layered with Hubble’s 31st-anniversary image of the stunning newborn nebula. Ionized hydrogen and nitrogen are shown in red here, while visible-spectrum images of dust reflecting starlight are shown in blue:
AG Carinae is a rarity, one of only fifty or so of its kind known to exist in the entire Local Group. It’s a very young star that will only live a few million years. The star’s mass is estimated at around seventy times the mass of our sun, but it shines a million times as bright. That enormous mass makes it unstable; the star sits at the center of a shell that it has hollowed out with its repeated explosions, forming an iris-like nebula as wide as the distance between Earth and Alpha Centauri. It will continue this tug-of-war between gravity and its own radiative force until it has finally cast off enough material to become stable.
For more on AG Carinae and its nebula, check out the ESA’s press release on this new analysis, which includes a nifty slider tool you can use to compare versions.
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