A galaxy spinning out of sync

Meta Title: NGC 4698: The Virgo Galaxy Spinning Out of Sync | ProductVortex
Meta Description: Hubble’s new view of NGC 4698 reveals a spiral galaxy with an unusually misaligned central structure, offering clues to gas accretion and past mergers.
URL Slug: ngc-4698-galaxy-spinning-out-of-sync
Excerpt: NGC 4698 looks like a conventional spiral galaxy at first glance. But its central stars and gas rotate on a different axis from the main disc, making it a rare example of a galaxy with a dynamically decoupled core.

## A familiar-looking spiral with an unusual interior

The NASA/ESA Hubble Space Telescope has captured a detailed view of NGC 4698, a spiral galaxy roughly 55 million light-years from Earth in the constellation Virgo.

At first sight, NGC 4698 appears relatively ordinary. It has a flattened disc, winding spiral arms, dark dust lanes, blue regions associated with young stars, and a brighter central bulge dominated by older stellar populations. These are all common features of spiral galaxies, including the Milky Way.

But astronomers have found that NGC 4698 is not rotating as a single, neatly aligned system.

Its central region is oriented and rotating differently from the galaxy’s larger stellar disc. The bulge appears to extend roughly at a right angle to the plane of the main disc, while stars and gas close to the nucleus move on an axis perpendicular to the outer galaxy’s rotation.

That unusual geometry makes NGC 4698 an important example of how galaxies can be reshaped by their environments and by encounters with other galaxies.

## NGC 4698 lies in the crowded Virgo Cluster

NGC 4698 is part of the Virgo Cluster, the nearest large galaxy cluster gravitationally bound to the Milky Way’s local region of the Universe.

The Virgo Cluster contains more than a thousand galaxies, from giant elliptical galaxies to smaller dwarf systems. Its crowded environment makes gravitational interactions more likely than they would be in a relatively isolated region of space.

Galaxies in clusters can be altered in several ways. Close passages can disturb their gas and stars. Small satellite galaxies can be absorbed. Gas can also be stripped away or, in some circumstances, captured from surrounding material. Over billions of years, these processes can change a galaxy’s shape, star-formation activity and internal motions.

NGC 4698 may preserve evidence of one of these events in its oddly oriented centre.

## What does “spinning out of sync” mean?

Most spiral galaxies have a broadly consistent arrangement: stars, gas and dust orbit in roughly the same plane around the galaxy’s centre. There can be warps, bars, rings and local disturbances, but the overall disc usually shares a common direction of rotation.

NGC 4698 is different because its central component is dynamically decoupled from the rest of the galaxy.

In practical terms, this means that material near the centre does not simply follow the rotation pattern of the broad outer disc. The inner stars and gas rotate on a substantially different axis. Observations indicate that this axis is close to perpendicular to the rotation of the main disc.

This is not merely a visual illusion caused by viewing angle. Measuring the motions of stars and gas through spectroscopy allows astronomers to detect which material is moving toward or away from Earth. These measurements reveal the galaxy’s unusual internal kinematics, or motion patterns.

The central structure is sometimes described as an orthogonally decoupled bulge or core. Such systems are rare among spiral galaxies.

## A likely clue: gas acquired from outside the galaxy

The leading explanation is that NGC 4698 acquired gas from an external source.

If a galaxy pulls in gas whose orbit is tilted relative to its existing disc, that incoming material does not necessarily settle into the same plane. Instead, it can form a new rotating structure at an angle to the older galaxy. Over time, some of that gas may collapse into dense clouds and create new stars, preserving the unusual orientation in a central stellar component.

There are two broad ways this could happen.

### Gas accretion

NGC 4698 may have captured gas from its surroundings or from another galaxy. The captured gas could have carried angular momentum in a direction different from the motion of NGC 4698’s original disc.

Angular momentum is a key factor in galaxy evolution. It describes the tendency of rotating matter to keep moving around a particular axis. When externally acquired gas has a different angular momentum direction, it can establish a misaligned or counter-rotating structure.

### A minor merger

Another possibility is a minor merger, in which a larger galaxy absorbs a much smaller companion.

ESA notes that observations have identified a short stream or “tail” of hydrogen extending from one side of NGC 4698. Such features can be signs of gravitational disturbance and may support the idea that the galaxy interacted with, or accreted, a smaller neighbour in the past.

However, a hydrogen feature alone is not definitive proof of one specific merger scenario. Gas tails can be produced through several types of interactions. Reconstructing a galaxy’s history requires combining images with measurements of stellar motions, gas velocities, chemical abundances and the distribution of faint surrounding material.

What is clear is that NGC 4698’s central structure likely did not form through the same quiet, aligned evolution as its outer disc.

## Hubble’s image shows different generations of stars

The new Hubble image also highlights the contrast between NGC 4698’s central bulge and its outer spiral arms.

The bulge has a diffuse, pale appearance because it is dominated by older, cooler stars. These stars generally emit more light at yellow, orange and red wavelengths than the massive, short-lived blue stars found in actively star-forming regions.

By contrast, the spiral arms contain blue patches and reddish features. The blue areas are associated with young, hot stars, while the red-brown lanes trace dust. Dust absorbs and scatters visible light, creating the dark, textured bands that outline portions of the galaxy’s spiral pattern.

The image therefore records several stages of galactic life at once: old stellar populations in the central bulge, dust and gas in the disc, and relatively recent star formation in the arms.

Near the centre lies a supermassive black hole with a mass millions of times that of the Sun. Evidence suggests that it is actively accreting, or drawing in, some surrounding gas. An actively growing black hole can release energy as infalling material heats up, although the supplied release does not indicate that NGC 4698 is among the most luminous or extreme active galaxies known.

## Why misaligned galaxies matter

Galaxies are often presented as stable islands of stars, but NGC 4698 shows that their histories can be far more complicated.

A galaxy’s present-day appearance may conceal ancient interactions. Even a spiral system that looks orderly in visible light can contain stars and gas that remember a past collision, a close encounter or the arrival of external material.

Studying systems like NGC 4698 helps astronomers test models of galaxy assembly. In those models, galaxies grow not only by forming stars from their own gas reserves, but also by merging with smaller galaxies and exchanging material with their surroundings.

Misaligned structures are especially useful because they are difficult to produce through simple, isolated evolution. Their orientation provides a physical clue that something arrived from outside the original system.

NGC 4698 also offers a nearby laboratory for understanding how such events affect central galactic regions. The relationship between inflowing gas, star formation and black-hole feeding remains an active area of research. A tilted central gas reservoir may influence where stars form and how efficiently material reaches the black hole.

## A reminder that galaxy evolution is ongoing

The Hubble observations used for this image came from programme 18103, led by principal investigator Thilker and focused on galaxies in the Virgo Cluster.

The image is visually striking, but its greater value is scientific context. NGC 4698 is not simply a photogenic spiral; it is a galaxy whose internal motions challenge the expectation that a disc and bulge should share one common rotational arrangement.

Its unusual centre may be the long-lived aftermath of a minor merger or external gas capture. While the available evidence supports that broad picture, the exact sequence of events that produced the perpendicular structure is still not fully established.

Future observations, particularly those mapping faint hydrogen, stellar motions and the galaxy’s outer halo, could help clarify how NGC 4698 acquired its distinctive, out-of-sync core.

## Authority sources (external links)

– [ESA’s Hubble image release on NGC 4698](https://www.esa.int/ESA_Multimedia/Images/2026/09/A_galaxy_spinning_out_of_sync)
– [NASA’s Hubble Space Telescope science overview](https://science.nasa.gov/mission/hubble/)
– [ESA’s Hubble mission page](https://www.esa.int/Science_Exploration/Space_Science/Hubble)
– [NASA/IPAC Extragalactic Database entry point for galaxy data](https://ned.ipac.caltech.edu/)
– [European Southern Observatory explainer on galaxy evolution](https://www.eso.org/public/science/galaxies/)

## Internal links (ProductVortex