With dozens of large telescopes scattered around the globe, some so high above it, you might think you’ve discovered everything in the sky.
The recent discovery of a giant cloud of gas floating near the Andromeda galaxy, one of the most extensively studied objects in the heavens, suggests that the sky still offers a vast amount of celestial real estate. The latest evidence to show This cloud has been hidden in plain sight for decades. And best of all, its origins are shrouded in mystery.
French amateur astronomer Yann Sainty discovered this cloud, more technically called a nebula, last August. With the advent of inexpensive and very high quality digital detectors, astrophotography has never been easier. This made him a newcomer among astronomy enthusiasts, in that he focused on one selected area of the sky, effectively shooting with very long exposures in hopes of spotting a faint blur there. A trend was born.
Sainty was targeting the region around Andromeda, a large spiral galaxy much like our own Milky Way, just 2.5 million light-years away. Its proximity, cosmologically speaking, has made it an attractive target for astronomers for more than a century. With its most obvious riches mapped, astronomers generally assumed what was left to discover were small individual objects within the galaxy itself.
What Sainty discovered defies such expectations. Nearly as big as Andromeda itself, a gigantic extended structure appeared right next to it. The nebula only materialized when Sainty used a filter to acquire an image. This filter blocks all light except the blue-green glow emitted by doubly-ionized oxygen (that is, oxygen atoms that have lost their two external electrons, which commonly occurs in giant gas clouds). increase. It was inherently human curiosity that drove the use of this filter. No large-scale map of the very deep sky around Andromeda had ever been created.
Despite its close proximity to one of the most famous objects in the sky, the structure of Sainty’s image was a complete surprise to him, and to other astronomers as well. During this same observation, he also took deep images using a different filter tuned for light from hydrogen atoms. Nothing matched the size and shape of the unique oxygen-rich nebula.
When he suspected it was some kind of artifact in his image (for example, reflected light from his telescope), Sainty enlisted the help of two other amateur astronomers, Marcel Drechsler and Xavier Strottner. After analyzing the data, they asked another accomplished amateur astronomer, Bray Falls, to make more observations with his own telescope. He saw the same nebula in his own data and independently confirmed the existence of the cloud.
Ultimately, observations from five telescopes in France, California, and New Mexico convinced Sainty and his collaborators that the object was real. It is now called the Strottner-Drexler Saint Object 1, or SDSO-1.
But the question still remains: what is it?
To find out, Sainty and his colleagues contacted professional astronomers for a deeper analysis.Published in the Journal of the American Astronomical Society research notes, Clues to the nebula’s origin remain very vague, but the team’s results are fascinating.
Astronomers have considered many possibilities, but for now, the gas cloud resists explanation. Its proximity to Andromeda in the sky strongly suggests some connection with the galaxy, with the clouds gently curving as if bulging out of the galaxy. None of these properties are definitive that physically bind the cloud to the galaxy, but both are certainly provocative. If there is, that means the cloud is tens of thousands of light years long, making it one of Andromeda’s largest coherent structures.
If it’s in Andromeda’s giant halo (a roughly spherical collection of stars that surrounds the galaxy), it could be gas blown away by a stream of stars there. But if so, we should also see large amounts of hydrogen, the main building block of stars. At least too few to detect.
The constellation Andromeda is moving toward the Milky Way, and SDSO-1 lies roughly in between them, providing another potential clue. Andromeda is so close to the Milky Way that the individual halos of the two galaxies may interact and collide with each other as they pass through space. Diffuse gas within the halos of the two galaxies is compressed during the collision, forming curved structures like bow waves from a ship moving through water. But then the clouds should not be visible near Andromeda. Instead, it appears in the sky about halfway between the Andromeda constellation and the center of the Milky Way. And this scenario still cannot explain the lack of hydrogen.
Another possibility is that this cloud is physically much smaller, but very close to us. So it’s the Milky Way nebula that happens to appear near Andromeda. A planetary nebula is a shell of gas that is ejected when a sun-like star is dying, and is usually rich in hydrogen and oxygen. Because the central star energizes the gas, these nebulae tend to appear bright in the light emitted by both elements. Again, it is puzzling that SDSO-1 does not contain hydrogen.
SDSO-1 may be the remnant of a Milky Way star that exploded as a supernova, but it should glow in ultraviolet light and radio waves. But searching for older observations of Andromeda, astronomers see nothing coming from clouds at other wavelengths, including X-rays, visible light, and infrared light.
As such, there is currently no known mechanism that fits all data. Inexplicably, this is also what scientists like. Solving puzzles is why we wanted to be scientists in the first place.
The fact that nothing so massive in our sky has ever been detected is surprising, if not completely surprising, to astronomers, as large telescopes tend to have narrow fields of view. , it is difficult to observe celestial bodies with a large apparent size. In particular, it is difficult to observe sprawling objects like his SDSO-1, which is three full moons wide in the sky. The larger equipment simply missed it and couldn’t see the forest for the trees.
Also, this cloud is very faint and requires a long exposure to be spotted. The total observation time for the discovery and confirmation images using only the double-ionizing oxygen filter was a staggering 160 hours. Even the filters and detectors used in professional observatories are designed to see differently than amateur telescopes. This also amplifies the difficulty of finding objects like SDSO-1. Equipped with an incredible 378-megapixel camera and oxygen filter, he could even use the 3.8-meter Canada-France-Hawaii telescope to shortly Empty spot where SDSO-1 sat and could not see anything. It’s an impressive device, but it wasn’t designed to see something that big and faint in the sky.
To solve this riddle, we need a spectrum that splits cloud light into smaller wavelength divisions, much like raindrops split sunlight into a rainbow. By carefully examining the spectrum of SDSO-1, the velocity of that gas can be determined by the Doppler effect (a slight blue shift in its color when the gas is approaching, and a red shift when it is moving away). . If the cloud is moving at the same speed as Andromeda, it’s likely part of that galaxy. The authors of this study report that such spectral observations are already underway, but until they are finished, the origin and behavior of this cloud will remain a mystery.
While SDSO-1 presents a challenge, it is also a ray of hope. It shows that there are still many treasures left in the sky. Appropriate tools must be used to reveal them.
This is an opinion and analysis article and the views expressed by the author or authors are not necessarily Scientific American.
