Gomez’s Hamburger Hides a Nursery for Wide-Orbit Giants

ALMA maps of Gomez’s Hamburger show a one-sided sulfur arc on a 900 au disk, sitting on a clump that may be a giant planet still in collapse. Charles Law, an assistant professor at the University of Minnesota and the project’s lead, published the work in The Astrophysical Journal after first showing it at the American Astronomical Society’s 247th meeting in January.

The burger nickname is 40 years old. The new result is a chemical test of how giant planets can assemble hundreds of au from a young star, a range where the usual core-growth path runs out of time.

The Burger Hubble Thought Was a Dying Star

Arturo Gómez, a support astronomer at the Cerro Tololo Inter-American Observatory in Chile, spotted the object in 1985 on sky photographs. A dark band cut across a pair of bright lobes, so the plates looked like a bun, a patty, and another bun, and the name stuck. Catalogued as IRAS 18059-3211, it sits in Sagittarius and was long read as a short-lived shell around a star that had already left the main sequence.

Hubble’s Wide Field Planetary Camera 2 imaged it on February 22, 2002, and the Heritage release on August 1, 2002, still billed Gomez’s Hamburger as a sun-like star nearing the end of its life, about 6,500 light-years away. The dark lane was the shadow of a thick disk seen edge-on, the star hidden inside, the “buns” only starlight bouncing off dust. That reading put the object in the brief proto-planetary-nebula phase, which lasts under a thousand years, and it was wrong.

Submillimeter Array maps of carbon monoxide in 2008 showed gas in Keplerian rotation around a young A-type star, not an expanding death shroud. Hubble’s own NICMOS scattered-light frames already had the flared geometry of a planet-forming disk. The burger was a birth site that had been filed with the obituaries.

HOW THE OBJECT CHANGED IDENTITY

1. 1985: Arturo Gómez finds a dark-banded nebula on Cerro Tololo plates and the hamburger name enters the literature.
2. August 1, 2002: Hubble Heritage presents the object as a dying star about 6,500 light-years away in Sagittarius.
3. 2008: SMA carbon monoxide maps show a rotating disk around a young A star, ending the planetary-nebula reading.
4. 2015: Very Large Telescope mid-infrared images isolate a cold southern clump, named GoHam b, as a gravitational-collapse candidate.
5. October 2022 to June 2024: ALMA Band 7 tracks at 0.9 mm resolve the vertical stack and the sulfur arc.
6. October 19, 2026: NRAO says the Law team’s paper is out in The Astrophysical Journal.

That last step is what moved the object off the curiosity list. The National Radio Astronomy Observatory posted the published result on October 20.

NEW: Cosmic “Hamburger” Has the Secret Ingredients

🍔 Hold the pickles! Just gas and dust for us, thanks.

Astronomers using @almaobs to study “Gomez’s Hamburger”—aka GoHam—discover the earliest phases of giant planet formation between its dense layers.https://t.co/aRRloHgZ3V pic.twitter.com/TMqDdnyDTo

— National Radio Astronomy Observatory | NSF NRAO (@TheNRAO) October 20, 2026

ALMA Cuts the Disk Into Gas and Dust Layers

Most planet-forming disks are tilted toward Earth, so height is squashed into a pancake. GoHam is close to edge-on, which splits the stack in the sky and lets a millimeter array read it like a cut cake. Law’s program (ALMA 2022.1.00269.S) combined a short-baseline track on October 15, 2022, with long-baseline tracks from June 5 to June 20, 2024, at about 0.2 arcseconds, or better than 30 au at the new distance.

The high-angular-resolution ALMA maps of the GoHam disk put millimeter-sized dust in a thin midplane ribbon, while the gas puffs far above and below it. Two forms of carbon monoxide and the sulfur-bearing molecule CS sit at different heights, matching the textbook layering of a cold outer disk, and the 0.9 mm continuum is a narrow lane with no clear rings or gaps at this resolution. A simple Gaussian fit gives an inclination of about 80 degrees as a lower limit, in line with earlier values near 85 degrees.

WHERE EACH TRACER SITS

12CO traces gas out to about 900 au in radius and as high as about 350 au, which still puts GoHam among the largest known planet-forming disks even after the distance was cut. The disk mass, Law’s team writes, can reach a few tenths of a solar mass, and the Toomre Q value sits at ≲2, the range where self-gravity starts to matter.

GoHam b Sits Under a One-Sided Sulfur Arc

The surprise is not the burger shape. It is a narrow, one-sided ribbon of sulfur monoxide that hugs the eastern edge of the bright dust and is much brighter in the south. Its motion still follows the disk’s rotation, so the gas has not been flung out. The peak lines up with a southern over-density first seen in 13CO and in a dip in 8.6 and 11.2 micron PAH glow, the clump called GoHam b, at a projected distance of about 280 au.

ALMA’s own press note described that one-sided arc of sulfur monoxide emission as lining up with material that may be collapsing under its own gravity. Older work treated GoHam b as a cold, dense clump of at least several Jupiter masses inside a region no larger than about 80 au. Models of gravitationally unstable disks, including work by John Ilee and colleagues, predict that collapsing fragments heat ices and spike gas-phase sulfur oxides such as SO, which is why Law’s team went after that line.

The combination of extreme disk size, strong asymmetries, winds, and potential planet formation makes it the perfect laboratory for understanding how giant planets can form far from their star, and how their presence reshapes the surrounding gas and dust.

Charles Law, assistant professor, University of Minnesota, NRAO statement

The paper is more careful than the press kit. Once ALMA resolved the disk, the old 13CO “extra blob” could no longer be read as a unique over-density without a full model of the warped, windy gas, and the authors say they do not try to confirm or refute GoHam b with these data. A companion study led by Jensen Lawrence at MIT is still building a three-dimensional reconstruction. What they do claim is that the SO arc traces localized heating tied to the same southern disturbance.

WHAT WE KNOW

• The sulfur arc: SO is confined to a narrow eastern ribbon, brighter in the south, and still in orbital motion with the disk.
• The alignment: The brightest SO sits on the southern dust excess, the old 13CO bump, and a one-sided gap in small-grain scattered light.
• The heating: Sulfur ices return to the gas at dust temperatures of about 20-70 K, and freeze-out times at outer-disk densities are only 100 to 1,000 years, so the arc needs ongoing or recent heat.

WHAT IS UNCONFIRMED

• A bound planet: GoHam b may be a bound fragment, a pre-fragment over-density, or part of a larger eccentric-disk pattern, and this ALMA paper does not decide.
• The Hill sphere: For a few Jupiter masses at 280 au the bound zone is only about 10-20 au across, smaller than the SO ribbon, so much of the glowing gas may be sheared disk material that passed through a hot wake.
• A unique trap: A vortex, a warp, or a lopsided eccentric disk could also pile southern dust without a planet in the middle.

Law still called the system a perfect laboratory for giant planets far from their star, and that claim does not need GoHam b to have finished collapsing. The chemistry is already doing the work that wide-orbit theory has been missing.

Giant Planets Should Not Form This Far From a Star

The standard path, core accretion, grows a rock-ice core then pulls on gas. It works well inside a few tens of au, where solids are dense and orbits are short. At hundreds of au the surface density of pebbles is low and the clock is slow, and the gas disk can drain before a core ever reaches the mass that triggers a runaway envelope. Direct-imaging surveys keep finding heavy companions on those wide tracks anyway, and HR 8799 is the textbook case: four giants on wide orbits around an A star, a layout core accretion alone has trouble growing before the gas is gone.

Gravitational instability is the other path. If a disk is cold and heavy enough, it can fragment into self-gravitating clumps that collapse on a dynamical time, about 1,000 years when the disk-to-star mass ratio is near 0.1, instead of millions. GoHam is an A star of 2.2 ± 0.5 solar masses with a disk that models still allow to reach a few tenths of a solar mass and a Q value at the fragmentation edge. GoHam b, if it is real, sits about nine times farther from its star than Neptune sits from the Sun. That is farther out than the HR 8799 planets, and it is exactly where collapse is supposed to beat core growth.

WHY THE OUTER DISK NEEDS A DIFFERENT PATH

• Time: Building a solid core at 280 au can outlast the gas, while a fragment can collapse in about 1,000 years.
• Mass budget: Cadman and colleagues have argued that disks around stars of 2 solar masses or more fragment at lower disk-to-star ratios than disks around Sun-like stars.
• Chemistry: An SMA survey led by Erin Cusson at MIT found 11 molecules in GoHam but no clean H2CO spike of shocks, so the new SO arc is the first chemical hint that collapse heating is actually running.

Olivier Berné’s 2015 VLT study already framed GoHam b as a possible precursor of the heavy planets seen around A stars such as HR 8799 and Beta Pictoris. The ALMA sulfur map is the first time that idea has a molecule attached to it. The burger joke is what travels. The sleeper is that this disk is how those wide giants might be born, in public, at millimeter wavelengths.

The Lopsided Patty That Traps Planet Food

The millimeter dust is not a clean patty. One side of the disk is brighter and more extended, with a narrow extra lane of dust running south, and Law’s team reads that as a vortex or a large-scale disturbance that can trap solids. The southern continuum also looks vertically thinner than the north, which could mean large grains have settled harder there, or that we are seeing a temperature and optical-depth trick along the edge-on line of sight.

The same southern side carries the PAH dip and the SO peak. In a fragmenting disk, spirals and clumps make local pressure bumps that catch millimeter grains, and simulations of heavy disks produce exactly that kind of one-sided, radially stretched dust pile. An eccentric disk, like the one proposed for the similarly large Dracula’s Chivito system, could pile dust near apocenter without a compact trap. A warp in the inner disk could throw a one-sided shadow that looks like a gap in scattered light. The paper leaves those doors open and asks for centimeter maps and a spectral-index image that would show whether the south is truly rich in large grains.

For planet growth the distinction matters less than the pile itself. Extra solids on one side are extra food, whether a vortex, a spiral, or a clump put them there, and GoHam already had more dust than typical disks around similar stars.

Starlight Is Stripping Gas From the Outer Disk

12CO and 13CO are not in pure orbital motion. Faint, wispy carbon monoxide runs north and far out, and the team reads that as a photoevaporative wind, starlight slowly lifting gas off the disk into space. The 12CO mask had to be stretched by hand to catch that northern haze, which is how you know it is not a textbook Keplerian disk.

A disk that is both fragmenting and evaporating is on a clock from two directions. Collapse wants dense gas to stay put. The wind wants the outer reservoir to leave. If GoHam b is a clump still gathering mass, it is doing so while the envelope around it thins. That is a messy laboratory, which is why Law listed winds next to size and lopsided dust as the reason to keep staring at this one object.

The SO gas itself may already be shearing away from whatever heated it. Adsorption onto grains at outer-disk densities takes 100 to 1,000 years, a slice of an orbit at 100-200 au, so a hot wake can light a crescent that is larger than the fragment that caused it. The arc is a scar, not a portrait of a finished planet.

How Far Is Gomez’s Hamburger From Earth?

The star is hidden by the dark lane, so Gaia-style parallax is ugly, and the distance has bounced for decades. Hubble’s 2002 write-up used about 6,500 light-years. Later disk papers often assumed 250 parsecs. Law’s team adopts a new value of 139 ± 24 parsecs from 3D dust-extinction maps, about 450 light-years, which puts GoHam on the outskirts of the Scorpius-Centaurus association.

That cut shrinks every physical scale that was tied to the old 250 parsec yardstick and lowers distance-dependent disk-mass estimates by a factor of a few. The 12CO radius is still about 900 au. GoHam b is still about 280 au out. The system is simply closer, so the same angles on the sky mean less raw mass and a cleaner chance that ALMA is resolving structure instead of smearing it.

GOHAM IN NUMBERS

• Distance: 139 ± 24 parsecs, about 450 light-years, about 14 times closer than Hubble’s 6,500 light-year figure.
• Star: Dynamical mass 2.2 ± 0.5 solar masses, surface temperature about 10,000 K, A-type pre-main sequence.
• Disk: 12CO out to about 900 au and up to about 350 au high, mass up to a few tenths of a solar mass, Q ≲ 2.
• GoHam b: About 280 au south, at least several Jupiter masses inside ≲80 au, still a candidate.

The closer distance is also why the hamburger is a practical target rather than a faint smudge. At 450 light-years, 0.2 arcseconds is a few tens of au, small enough to put the sulfur arc next to the dust lane instead of blending them. The dying-star file is closed. The open file is whether that southern clump will finish collapsing, shear apart, or migrate, and the next maps from Law’s group will have to answer that in three dimensions.

Frequently Asked Questions

Where is the ALMA array that mapped Gomez’s Hamburger?

ALMA is a partnership of the European Southern Observatory, the U.S. National Science Foundation, and Japan’s National Institutes of Natural Sciences, working with Chile, and the dishes sit in the Atacama Desert. North American operations run through the National Radio Astronomy Observatory, managed by Associated Universities, Inc. The GoHam data used Band 7 near 0.9 mm, with 44 antennas on the first track and 43 to 45 on the long-baseline tracks.

What is an astronomical unit in this disk?

One au is the Earth-Sun distance, about 150 million kilometers. Neptune orbits at 30 au, so GoHam’s carbon monoxide disk, at about 900 au in radius, reaches 30 times that far, and the GoHam b clump at about 280 au is still nine times Neptune’s orbit. Press copy sometimes rounded the gas to almost 1,000 au; the paper’s scaled 12CO extent is about 900 au.

How fast can a disk fragment become a giant planet?

In the gravitational-instability path, a clump can collapse on a dynamical time of about 1,000 years when the disk-to-star mass ratio is near 0.1, far shorter than the millions of years core accretion can need in the outer disk. That speed is the reason wide-orbit giants around A stars are often blamed on fragmentation. It is also why a sulfur arc that can freeze back out in 100 to 1,000 years is a useful clock: the heat source has to be recent.

Why do edge-on disks help more than face-on ones?

In a face-on disk, gas at different heights is stacked along the same line of sight, so a bright ring can mix a hot surface with a cold midplane. An edge-on disk spreads those layers across the sky, so 12CO, 13CO, CS, and dust can be assigned real heights instead of inferred ones. GoHam is one of the few large, gas-rich disks sitting that way, which is why Law’s group used it as a benchmark even before the sulfur arc showed up.