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Something is killing galaxies — and science is on the case

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In the most extreme regions of the universe, galaxies are being killed. Their star formation is being shut down and astronomers want to know why.

The first ever Canadian-led large project on one of the world’s leading telescopes is hoping to do just that. The new program, called the Virgo Environment Traced in Carbon Monoxide survey (VERTICO), is investigating, in brilliant detail, how galaxies are killed by their environment.

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As VERTICO’s principal investigator, I lead a team of 30 experts that are using the Atacama Large Millimeter Array (ALMA) to map the molecular hydrogen gas, the fuel from which new stars are made, at high resolution across 51 galaxies in our nearest galaxy cluster, called the Virgo Cluster.

Commissioned in 2013 at a cost of US$1.4 billion, ALMA is an array of connected radio dishes at an altitude of 5,000 metres in the Atacama Desert of northern Chile. It is an international partnership between Europe, the United States, Canada, Japan, South Korea, Taiwan and Chile. The largest ground-based astronomical project in existence, ALMA is the most advanced millimetre wavelength telescope ever built and ideal for studying the clouds of dense cold gas from which new stars form, which cannot be seen using visible light.

Large ALMA research programs such as VERTICO are designed to address strategic scientific issues that will lead to a major advance or breakthrough in the field.

Galaxy clusters

Where galaxies live in the universe and how they interact with their surroundings (the intergalactic medium that surrounds them) and each other are major influences on their ability to form stars. But precisely how this so-called environment dictates the life and death of galaxies remains a mystery.

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Galaxy clusters are the most massive and most extreme environments in the universe, containing many hundreds or even thousands of galaxies. Where you have mass, you also have gravity and the huge gravitational forces present in clusters accelerates galaxies to great speeds, often thousands of kilometres-per-second, and superheats the plasma in between galaxies to temperatures so high that it glows with X-ray light.

In the dense, inhospitable interiors of these clusters, galaxies interact strongly with their surroundings and with each other. It is these interactions that can kill off — or quench — their star formation.

Understanding which quenching mechanisms shut off star formation and how they do it is main the focus of the VERTICO collaboration’s research.

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The life cycle of galaxies

As galaxies fall through clusters, the intergalactic plasma can rapidly remove their gas in a violent process called ram pressure stripping. When you remove the fuel for star formation, you effectively kill the galaxy, turning it into a dead object in which no new stars are formed.

In addition, the high temperature of clusters can stop hot gas cooling and condensing onto galaxies. In this case, the gas in the galaxy isn’t actively removed by the environment but is consumed as it forms stars. This process leads to a slow, inexorable shut down in star formation known, somewhat morbidly, as starvation or strangulation.

An image of spiral galaxy NGC 4330 in the Virgo Cluster. Ram pressure stripped hot gas is shown in red and a blue overlay shows star-forming gas.
Fossatie et al. (2018), Author provided

While these processes vary considerably, each leaves a unique, identifiable imprint on the galaxy’s star-forming gas. Piecing these imprints together to form a picture of how clusters drive changes in galaxies is a major focus of the VERTICO collaboration. Building on decades of work to provide insight into how environment drives galaxy evolution, we aim to add a critical new piece of the puzzle.

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An ideal case study

The Virgo Cluster is an ideal location for such a detailed study of environment. It is our nearest massive galaxy cluster and is in the process of forming, which means that we can get a snapshot of galaxies in different stages of their life cycles. This allows us to build up a detailed picture of how star formation is shut off in cluster galaxies.

Galaxies in the Virgo cluster have been observed at almost every wavelength in the electromagnetic spectrum (for example, radio, optical and ultra-violet light), but observations of star-forming gas (made at at millimetre wavelengths) with the required sensitivity and resolution do not exist yet. As one of the largest galaxy surveys on ALMA to date, VERTICO will provide high resolution maps of molecular hydrogen gas — the raw fuel for star formation — for 51 galaxies.

With ALMA data for this large sample of galaxies, it will be possible to reveal exactly which quenching mechanisms, ram pressure stripping or starvation, are killing galaxies in extreme environments and how.

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By mapping the star-forming gas in galaxies that are the smoking gun examples of environment-driven quenching, VERTICO will advance our current understanding of how galaxies evolve in the densest regions of the Universe.

[ Deep knowledge, daily. Sign up for The Conversation’s newsletter. ]The Conversation

Toby Brown, Post Doctorate Fellow in Astrophysics, McMaster University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Kanye ripped for latest Trump defense: Always someone willing to write a check to ‘a black person defending white supremacy’

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Kanye West hugging Trump

A panel discussion on recent concerts put on by Kanye West in Salt Lake City and Howard University turned to his new recent comments he made defending his support for Donald Trump -- with one panelist saying the rapper is getting paid on the side for siding with the president.

Speaking with host Kendis Gibson, guests Danielle Moodie-Mills and Clay Cane were harshly critical of West trying to drum up black support for the president as well as his recent comments on slavery.

"What is going on here?" Gibson began. "So you saw the pictures of Kanye West in the middle of Salt Lake City. He drew about 10,000 people here at Howard University, it was a smaller crowd because they didn't get the e-mail about it until 6:00 a.m. on homecoming weekend. Largely, a lot of people who are going to these shows are black folks. These are some of the scenes in Salt Lake City, so people are wondering: is he sort of like Trump's secret weapon, a secret outreach to the black community? "

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Here are 3 moves a desperate Trump will likely attempt in order to cling to power

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In a column for the Daily Beast, political observer Micheal Tomasky speculated -- and not without good reason -- that a frantic Donald Trump will do anything to remain in office and thereby avoid being slammed with criminal indictments once he departs the Oval Office for good..

As the columnist explained, impeachment seems inevitable and the president will likely take desperate measures and that he has already given hints about three paths he may take -- if not all of them.

Tomasky wrote, "It’s foolish to say that Trump thinks ahead about anything. The late journalist Wayne Barrett said many true things about Trump, but the truest ever was when he observed that Trump says whatever will get him through the next 10 minutes," before adding, "People around him of course are more strategic and are thinking ahead. And they’re all saying and doing and writing things right now that will, if the opportunity presents itself, pave the way for Trump to burn the Constitution."

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Pentagon says up to 1,000 US troops to withdraw from northern Syria

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The Pentagon said Sunday President Donald Trump had ordered the withdrawal of up to 1,000 troops from northern Syria -- almost the entire ground force in war-torn country -- amid an intensifying Turkish assault on Kurdish forces.

Defense Secretary Mark Esper said the move came after the US learned that Turkey was pressing further into Syria than had been expected.

And the Kurdish-led Syrian Democratic Forces (SDF) are seeking a deal with the Syrian regime and Russia to counter-attack against the Turks in the north, Esper added.

"We find ourselves as we have American forces likely caught between two opposing advancing armies and it's a very untenable situation," Esper told CBS's Face the Nation.

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