Regardless of being one of the crucial venerable and distinguished objects within the evening sky, the Andromeda Galaxy (M31) nonetheless has surprises. And a gaggle of novice astronomers have uncovered the most recent: a beforehand unknown emission nebula mendacity simply southeast of Andromeda and spanning half the width of the galaxy itself.
The characteristic was found in photographs taken final 12 months with an Oxygen-III (OIII) filter by French astroimager Yann Sainty, who labored with Marcel Drechsler and Xavier Strottner to course of and analzye the information. They’ve designated the characteristic Strottner-Drechsler-Sainty Object 1.
They then labored with a group {of professional} astronomers and different astroimagers to substantiate the discover. The group revealed their leads to Research Notes of the AAS final month — in addition to a shocking, highly-processed picture on the astroimaging website Astrobin (reproduced above).
A facet venture
The observations of Andromeda started as a facet venture for the trio, who had initially teamed up for an additional purpose: Drechsler and Strottner preserve a catalog of planetary nebulae, and had requested Sainty to seize a number of recognized and candidate objects.
Sainty traveled all throughout France seeking the darkest websites he may discover for his cellular observing setup, which features a 4.2-inch Takahashi refractor and a CMOS astronomical digital camera from ZWO. After concluding this months-long venture, Sainty “determined to deal with a soothing and straightforward venture — the Andromeda Galaxy,” Drechsler mentioned in an announcement shared with media, together with Astronomy and ZWO.
“Whereas engaged on the Andromeda venture, Yann Sainty did one thing that few astrophotographers earlier than him have executed — he used an OIII filter to raised deliver out the faint HII areas,” mentioned Drechsler. “Since an OIII filter is comparatively new territory in astrophotography, Yann despatched the information to [me] and Xavier for assessment. Yann’s secret hope, maybe, was to have a beforehand unknown planetary nebula or supernova remnant within the knowledge.”
When Drechsler and Strottner appeared on the OIII photographs, they seen “an especially faint nebulosity … on the fringe of the picture that appeared to proceed exterior the photograph.” At first, the group thought-about whether or not it was an artifact, like a gradient launched by means of a defective flat-field calibration picture. However Drechsler “urged Sainty to gather extra OIII knowledge, considering he noticed finer sub-structures within the barely-visible nebula.”
Sainty collected extra photographs by means of the autumn of 2022, finally totaling 111 hours of publicity. As he did, the group started more and more positive that they had discovered one thing actual — and beforehand unreported.
Confirming observations
The group reached out to skilled astronomers to assist in verifying their discovery, together with Robert Fesen of Dartmouth Faculty in Hanover, New Hampshire. In an interview with Astronomy finally month’s assembly of the American Astronomical Society (AAS) in Seattle, Fesen pointed to the arc in a picture and summed up his preliminary response: “What the hell is that?”
“After they despatched it to me, I mentioned, ‘There’s one thing mistaken along with your digital camera, and go repair it and depart me alone,’” he quipped. “[Dreschler] got here again a few weeks later: ‘Rob, it’s actual.’ And I mentioned, ‘Look, you haven’t tried exhausting sufficient to kill it.’”
To substantiate it, different astroimagers joined the hunt: Bray Falls working with two distant telescopes in California, Christophe Vergnes and Nicolas Martino in France, and Sean Walker (affiliate editor at Sky and Telescope journal) observing with a distant telescope in New Mexico. Their outcomes satisfied Fesen: “5 totally different telescopes see stuff there? At totally different ranges of decision, however it’s in the identical spot of the sky off M31? I made a decision it’s actual.”
Remarkably, the nebula had been missed by earlier OIII surveys of M31 on professional-grade telescopes, including one by the three.6-meter Canada-France-Hawaii Telescope (CFHT) on Mauna Kea. That’s as a result of many devices designed for analysis merely aren’t well-suited to identify such a faint and prolonged nebula.
CFHT’s MegaCam instrument has a area of view of 1° — extensive by skilled requirements, however nonetheless not extensive sufficient to seize the total extent of the brand new object, which spans 1.5°. The MegaCam survey of M31 additionally used a filter that allowed a comparatively wide selection of wavelengths to go by means of — over 10 nanometers. Sainty used an off-the-shelf Antlia filter with a bandwidth of simply 3 nm, which higher remoted the OIII sign from background noise.
Right here or there?
The discover has set the astronomical group ablaze with hypothesis in regards to the object’s nature, together with whether or not it’s bodily subsequent to Andromeda, which is 2.5 million light-years away. It’s totally potential that the newfound object is a part of the Milky Way and easily lies alongside our line of sight to our galactic neighbor.
One risk that the group thought-about was that the characteristic is brought on by Andromeda starting to work together with the Milky Way. However, they wrote, “the arc appears a lot too near M31 to suit that image. Extra doubtless, it lies inside M31’s halo and is expounded to the quite a few stellar streams, particularly the Big Stellar Stream whose japanese edge lies near the OIII arc.”
Nonetheless, Fesen tells Astronomy that since then, “I’ve began to suppose it much less prone to be a characteristic of M31, however, as a substitute, a Milky Way nebula a lot nearer. However who is aware of.”
To settle the difficulty, Fesen and his colleagues hope to acquire a spectrum with a professional-grade observatory. From this, they will measure any Doppler shift within the mild brought on by movement towards or away from the Milky Way — and whether or not it matches the movement of Andromeda itself.
Whether or not or not the arc is in the end related to Andromeda, the invention highlights the function that novice astronomers and imagers with extensively out there high-quality narrowband filters are taking part in in discovering faint, prolonged emission nebulae.
Fesen expressed admiration for the imagers, who, he notes, are taking knowledge that totals exposures of “fractions of a day or extra.” He pointed to one of many affirmation photographs: “That one image’s 86 hours. Are you kidding me? [Sainty’s image] was taken over 22 nights over three months of clear climate. That is insane.”
