The night sky showcases untold astronomical riches.
Behind the dome of a series of European Southern Observatory telescopes, the Milky Way towers in the southern skies, flanked by the Large and Small Magellanic Clouds, at right. Although there are several thousand stars and the plane of the Milky Way all visible to human eyes, the most distant objects we can see all lie far beyond our own home galaxy.
Credit: ESO/Z. Bardon (www.bardon.cz)/ProjectSoft (www.projectsoft.cz)
Closest is our Moon, whose
distance was approximated 2000+ years ago.
This diagram shows the Earth and Moon, as well as the distance between them, to scale. Two observers located on opposite sides of the Earth at the same time, one seeing the Moon rise and one seeing the Moon set, would see the Moon’s apparent position shifted by about 1.9 degrees relative to one another. This allows us to infer the Earth-Moon distance.
The Moon and planets sometimes occult stars, demonstrating that stars are farther.
When one astronomical object occupies the same line-of-sight as another, an occultation will occur, as the “closer” object blocks the light that would otherwise be visible from the “farther” object. The Moon occults all of the other planets; the Moon and planets occult background stars, revealing the relative distances between them.
Credit: Bob King/Stellarium/Sky & Telescope
in 964 CE, the Andromeda galaxy outdistances any object in our Milky Way.
This 1888 image of the Andromeda Galaxy, by Isaac Roberts, is the first astronomical photograph ever taken of another galaxy. It was taken without any photometric filters, and hence all the light of different wavelengths is summed together. Every star that’s part of the Andromeda galaxy has not moved by a perceptible amount since 1888, a remarkable demonstration of how far away other galaxies truly are. Although Andromeda is a naked-eye object under even modestly dark skies, it was not recorded until the year 964, and was not shown to be extragalactic until 1923.
Credit: Isaac Roberts
It wasn’t until 1923, however, that
measurements of internal variable stars proved its extragalactic nature.
Perhaps the most famous photographic plate in all of history, this image from October of 1923 features the great nebula (now galaxy) in Andromeda along with the three novae that Hubble observed within them. When a fourth brightening event happened in the same location as the first, Hubble recognized this was no nova, but a Cepheid variable star. The “VAR!” written in red pen was Hubble having a spectacular realization: this meant Andromeda was an extragalactic object, located far beyond the Milky Way.
Credit: Carnegie Observatories
By that time, many more distant objects had been observed.
Spirals, initially recorded as faint, fuzzy objects with no discernible structure through more primitive telescopes, were clearly observed since the mid-1800s to be prevalent in the night sky. But their nature was a mystery, and a democratic attempt to settle the issue in 1920 only raised more unanswered questions. It wasn’t until 1923, and the identification of individual stars within one of them (Andromeda), that their extragalactic nature began to be understood.
Credit: ESO/P. Grosbøl
Triangulum galaxy, recorded in 1654, is our farthest naked-eye object.
The spiral galaxy Messier 33, shown as imaged by an amateur astronomer with X-ray data from NASA’s Chandra overlaid in pink, is also known as the Triangulum galaxy: a faint galaxy visible in the southern skies. First recorded in 1654, it is the faintest object visible by typical, unaided human eyes.
Credit: Optical: Warren Keller; X-ray: NASA/CXC/SAO/P. Plucinsky et al.
In 1779, spiral galaxy
Messier 58 broke that record.
Galaxy Messier 58, recorded in 1779 by Charles Messier, is the most distant galaxy in the Messier catalog at 62 million light-years distant. Although its distance and nature were unknown to Messier (and to others for over 100 years after its discovery), it was, for a time, the most distant object discovered and viewed by humanity.
Credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona
In 1785, William Herschel found giant elliptical
Giant elliptical galaxy NGC 584, shown here, was discovered and recorded in 1785, and is located approximately 62 million light-years away. Although it was not known to be an extragalactic object until the 1920s, it was briefly the most distant object known and recorded until NGC 1 was identified a few months later.
Credit: Sloan Digital Sky Survey
NGC 1 broke the 100 and 200 million light-year barriers.
Galaxy NGC 1, at top, was the first object recorded in William Herschel’s general catalog from 1786, but was not re-recorded until the 1860s. Its distance of 211 million light-years made it the most distant object known and recorded for around a century, although the much fainter NGC 2, located below it, is nearly twice as distant.
Credit: DESI Legacy Surveys / Dustin Lang (Perimeter Institute)
First appearing on photographic plates
from 1887, OJ 287 is presently measured at 3.5 billion light-years away.
The most massive pair of black holes in the known Universe is OJ 287, whose gravitational waves will be out of reach of LISA. A longer-baseline gravitational wave observatory could see it, as could, potentially, a sufficiently precise pulsar timing array. Although OJ 287 was first imaged in 1887, its nature and distance were not determined until the 1960s.
Credit: Ramon Naves/Observatorio Montcabrer
Before its distance was known, bright galaxies in clusters — like
Coma, Boötes, and Hydra — held the record.
This view of the Gemini Cluster of galaxies, taken in 1975, contains the galaxy known as LEDA 20221 (MCG+06-16-021), which is the brightest galaxy within that cluster. The brightest galaxy within that cluster was discovered in 1932, and with a distance in excess of 1 billion light-years from us, was the first object discovered to cross that vaunted threshold.
Credit: NOIRLab/AURA/NSF; KNPO 4-meter Mayall telescope
In the 1960s,
radio galaxies and quasars eclipsed those distances.
As shown with Chandra X-ray data (left) and with contours of radio data from the Very Large Array (right), quasar 3C 9 broke the cosmic distance record in 1965 and became the first object with a redshift of 2 or greater and is located at a distance of 16 billion-light years. Although many more quasars would extend that record, it wouldn’t be until 1997 that galaxies re-took the record from quasars.
Credit: A. C. Fabian, A. Celotti, & R. M. Johnstone, MNRAS, 2003
re-take the record until 1997.
The galaxy cluster shown here, CL 1358+62, is presently lensing two much more distant background galaxies, as shown in the white box by their red arcs. Those two objects, discovered on July 31, 1997 by Marijn Franx and Garth Illingsworth, broke the cosmic distance record at the time and became the first galaxies to be the cosmic record-holder for distance since 1960, when quasars first usurped them.
Credit: M. Franx (U. Groningen) & G. Illingworth (UCSC), WFPC2, HST, NASA
In 2009, gamma-ray burst
GRB 090423 became the most distant.
This false-color image, taken in the infrared with the GROND instrument at the MPI/ESO 2.2m telescope on La Silla in Chile, reveals the afterglow and redshift/distance of the spectacular April 23, 2009 gamma-ray burst GRB 090423. From 2009-2015, it was the most distant object ever discovered.
Credit: Jochen Greiner/GROND – Gamma-Ray Burst Optical/Near-Infrared Detector
EGSY8p7 and then GN-z11 were even farther.
Only because the most distant galaxy spotted by Hubble, GN-z11, is located in a region where the intergalactic medium is mostly reionized, was Hubble able to reveal it to us at the present time, breaking the prior record held by EGSY8p7. Other galaxies that are at this same distance but aren’t along a serendipitously greater-than-average line of sight as far as reionization goes can only be revealed at longer wavelengths, and by observatories such as JWST. At present, GN-z11 has been relegated to the 9th most distant galaxy known as of 2024: in the JWST era.
Credit: NASA, ESA, P. Oesch and B. Robertson (University of California, Santa Cruz), and A. Feild (STScI)
Finally, in 2022, JWST’s
JADES-GS-z13-0 surpassed them all.
The four most distant galaxies identified as part of JADES, thus far, include three that surpass the threshold for “most distant galaxy” previously set by Hubble. With no more than a quarter of the total JADES data taken thus far, this record will likely fall again, perhaps multiple times, over the coming months and years, but the unambiguous feature of the Lyman break can clearly be seen. The most distant, JADES-GS-z13-0, took the record from Hubble in December of 2022, and still holds it today. Although these are among the youngest galaxies ever discovered, their stellar populations are not pristine.
Credit: NASA, ESA, CSA, M. Zamani (ESA/Webb), Leah Hustak (STScI); Science credit: Brant Robertson (UC Santa Cruz), S. Tacchella (Cambridge), E. Curtis-Lake (UOH), S. Carniani (Scuola Normale Superiore), JADES Collaboration
clumps of neutral, spin-flipping hydrogen will outstrip any galaxy, distance-wise.
Whenever a neutral hydrogen atom forms, the electron within it will spontaneously de-excite until it’s in the lowest (1s) state of the atom. With a 50/50 chance of having those spins of the electron and proton aligned, half of those atoms will be able to quantum tunnel into the anti-aligned state, emitting radiation of 21 centimeters (1420 MHz) in the process. This should allow us to probe clumps of neutral hydrogen even farther back than the existence of the first stars.
Credit: SKA Organisation
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words.