Our Galaxy Appears to Be Part of a Structure So Large It Challenges Our Current Models of Cosmology

Astronomers have discovered that the Milky Way might be just a small piece of a much larger cosmic structure than previously believed. If confirmed by future observations, this research could suggest that our current model of how the universe evolves is still missing some crucial pieces.

"It is perhaps unsurprising that the further into the cosmos we look, we find that our home supercluster is more connected and more extensive than we thought."

As we study the universe more, we have found ourselves to be part of much larger structures, formed by gravitational interactions. We orbit the Sun, the Sun is part of the Milky Way, and the Milky Way is part of the Local Group, which includes several small galaxies as well as Andromeda, of "it may collide with us" fame.

But it doesn't stop there. The Local Group is on the outer edge of the Virgo Supercluster, which is itself part of a giant basin known as Laniakea. According to the new study, Laniakea too resides within a larger "basin of attraction" (BoA), potentially 10 times its volume.

"The entire Universe can be considered a patchwork of abutting BoA, just as the terrestrial landscape is separated into watersheds," the team explains in their paper. "A BoA is generally not gravitationally bound because the relative motion of distant points within it is usually dominated by cosmic expansion."

The basins of attraction are enormous structures, so much so that gravity is not the dominant force, but there is nevertheless evidence of common flow. The team looked at the motions of 56,000 galaxies, and attempted to make a "probabilistic map" of the local universe, given errors that occur when attempting to measure the velocity and motion of galaxies. In doing so, they hoped to narrow down the possibility of the existence of these basins of attraction.

“Our universe is like a giant web, with galaxies lying along filaments and clustering at nodes where gravitational forces pull them together,” University of Hawai'i at Manoa astronomer R. Brent Tully explained in a statement. “Just as water flows within watersheds, galaxies flow within cosmic basins of attraction. The discovery of these larger basins could fundamentally change our understanding of cosmic structure.”

“Our universe is like a giant web, with galaxies lying along filaments and clustering at nodes where gravitational forces pull them together,” University of Hawai'i at Manoa astronomer R. Brent Tully explained in a statement. “Just as water flows within watersheds, galaxies flow within cosmic basins of attraction. The discovery of these larger basins could fundamentally change our understanding of cosmic structure.”

Running simulations on the data, they found that the BoA encompassed many gigantic structures, including the mysterious Great Attractor.

"Nearby, evidence emerges for a BoA centred in proximity to the highly obscured Ophiuchus cluster that lies behind the centre of the Milky Way Galaxy," the team explained. "This BoA may include the so-called Great Attractor region and the entity Laniakea, including ourselves. In the extension [...] the Sloan Great Wall and the associated structure are overwhelmingly dominant."

Creating such maps of the universe is a messy business, tracking the movement of galaxies and their effect on each other in order to model these cosmic "currents" and flows. As such, there is a lot of uncertainty. According to the team's simulations, there is a 60 percent chance that our own Milky Way is in fact not in Laniakea, but in the Shapley concentration.

As well as being nice to really nail down our home address, the study could have much larger implications for our models of the universe, if the same structure continues to be found with further observation and analysis. Simply put, structures of gargantuan size challenge our understanding of the cosmos. 

Given what we see in the cosmic microwave background, the first light we can detect after the inflation of the universe, structures can only grow so large within our current models. Yet this, and other similar discoveries, appear to be larger than our current models predict. For now, the team plans to continue mapping the largest structures in the cosmos. 

"It is perhaps unsurprising that the further into the cosmos we look, we find that our home supercluster is more connected and more extensive than we thought," Noam Libeskind, astronomer at the Leibniz Institute for Astrophysics Potsdam, said in a separate statement. "Discovering that there is a good chance that we are part of a much larger structure is exciting. At the moment it’s just a hint: more observations will have to be made to confirm the size of our home supercluster."

Astronomers find giant hidden molecular cloud fueling star birth in Milky Way

 

The location of the area of focus for this research in the Milky Way galaxy is shown above, along with a previously unknown maser. Credit: Image credits as noted, collage created by NSF/AUI/NSF NRAO/P. Vosteen

An international team of astronomers has discovered a massive cloud of gas and dust located in a little-known region of our Milky Way galaxy. The Giant Molecular Cloud (GMC) is about 60 parsecs—or 200 light years—long.

In a new study published in The Astrophysical Journal, researchers using the U.S. National Science Foundation Green Bank Telescope (NSF GBT) have peered into a molecular cloud known as M4.7-0.8, nicknamed the Midpoint cloud. Their observations have revealed a dynamic region bustling with activity, including potential sites of new star formation.

"These dust lanes are like hidden rivers of gas and dust that are carrying material into the center of our galaxy..."

"One of the big discoveries of the paper was the GMC itself. No one had any idea this cloud existed until we looked at this location in the sky and found the dense gas. Through measurements of the size, mass, and density, we confirmed this was a giant molecular cloud," shares Natalie Butterfield, an NSF National Radio Astronomy Observatory (NSF NRAO) scientist and lead author of this paper.

"These dust lanes are like hidden rivers of gas and dust that are carrying material into the center of our galaxy," explained Butterfield. "The Midpoint cloud is a place where material from the galaxy's disk is transitioning into the more extreme environment of the galactic center and provides a unique opportunity to study the initial gas conditions before accumulating in the center of our galaxy."

The NSF GBT observations focused on molecules like ammonia (NH3) and cyanobutadiyne (HC5N), which are tracers of dense gas. Besides revealing the previously unknown Midpoint cloud in the galaxy's inward-bound dust lane, the data also showed:

• A New Maser: The team discovered a previously unknown "maser," a natural source of intense microwave radiation, associated with ammonia gas. This is often a sign of active star formation.

• Potential Star Birth Sites: The cloud contains compact clumps of gas and dust that appear to be on the verge of forming new stars. One of these clumps, dubbed Knot E, might be a frEGG (free-floating evaporating gas globule)—a small, dense cloud being eroded by radiation from nearby stars.

• Evidence of Stellar Feedback: The team found a shell-like structure within the cloud, possibly created by the energy released from dying stars.

• Turbulent Gas: The gas within the cloud is highly turbulent, similar to what is seen in the galaxy's central regions. This turbulence could be caused by the inflow of material along the dust lanes or by collisions with other clouds.

"Star formation in galactic bars is a bit of a puzzle," said Larry Morgan, a scientist with the NSF Green Bank Observatory (NSF GBO), "The strong forces in these regions can actually suppress star formation. However, the leading edges of these bars, such as where the Midpoint is located, can accumulate dense gas and trigger new star formation."

The team's findings suggest that the Midpoint cloud is a crucial link in the flow of material from the Milky Way's disk to its center. By studying this region, astronomers can learn more about how galaxies build their central structures and form new stars in extreme environments.