
Orange on the moon (nhỏ như chụp hình quả cam trên mặt trăng)
The Event Horizon Telescope initially set out to snag an image of the supermassive black hole at the core of our galaxy, the Milky Way. Called Sagittarius A*, that black hole is relatively puny compared to M87, containing the mass of just four million suns. Because M87 is one of the nearest, biggest black holes, the team also decided to aim the telescope there, hoping to eventually compare the two bruisers.
Seeing into the heart of our galaxy turned out to be a bit more complicated than staring down the barrel of a black hole in the next galaxy cluster over, which is why M87’s portrait is out first.
Rather than being a single snapshot, like the many spectacular photos taken by the Hubble Space Telescope, the EHT‘s image is the product of a process called interferometry, which combines observations from multiple telescopes into one image. When separate dishes simultaneously observe the same target, scientists can collate the observations and “see” an object as though they’re using one giant dish that spans the distance between those telescopes.
To resolve these supermassive black holes—which are tiny compared to their surrounding galaxies—the consortium needed to harness the power of radio telescopes all over the planet. In the end, six observatories in Mexico, Hawaii, Arizona, Chile, and Spain aimed their eyes into sky and stared at M87, which is the biggest galaxy in the center of the Virgo cluster. Functioning as one Earth-sized telescope, the network can resolve objects just one-ten thousandth the angular size of what Hubble can see.
“What we’re trying to image is really, really small on the sky,” says Caltech’s Katie Bouman, a member of the EHT imaging team. “It’s about the same size as if you were trying to take a picture of an orange on the moon.”
For several days, the team observed M87 in short radio wavelengths, because radio waves can pierce the murky shrouds of dust and gas surrounding galactic centers. During that observing run, which also included targets other than M87, the team gathered so much data—five petabytes—that the only reasonable way to transfer it was by shipping actual hard drives, rather than sending it digitally.
“Five petabytes is a lot of data,” says team member Dan Marrone of the University of Arizona. “It’s equivalent to 5,000 years of MP3 files, or according to one study I read, the entire selfie collection over a lifetime of 40,000 people.”
Then, because combining observations from different observatories is no simple task, four teams processed the data independently, using different algorithms and testing it against different models. In the end, the images each team produced were very similar, suggesting that the observations are robust and that the final snapshot is the most accurate possible. To be sure, it looks almost indistinguishable from simulations the team had produced in the years leading up to its release.
“It’s almost scarily as we predicted,” says EHT team member Sera Markoff of the University of Amsterdam. “I kept pulling it up on my phone at odd hours and looking at it.”
Soon, the team plans to share an image of the supermassive black hole nearest and dearest to Earth—but just because Sagittarius A* is closer, don’t expect it’s picture to look much sharper than the one they’ve already got.
“M87 is about two thousand times farther away, but its black hole is about two thousand times bigger,” says Lord Martin Rees of the University of Cambridge, who is the U.K.’s astronomer royal. “They’re the same angular size on the sky.”
……To Be Continues
Highlight Vocabulary
1.Snag (v) /snæg/ chụp lại
Telescope snag an image of the supermassive black hole.
(Kính viễn vọng chụp một hình ảnh của lỗ đen siêu lớn)
2.Puny (adj) /´pju:ni/ Nhỏ bé, yếu đuối, kém phát triển
puny limbs
(tay chân yếu ớt)
3.cluster (v) /’klʌstə/ Tụ họp lại, tụm lại
children cluster round their mother
(con cái tụm lại quanh mẹ)
4.Interferometry (noun) /¸intəfe´rɔmetri/ giao thoa
axial slab interferometry
(đo giao thoa bản hướng trục)
5.Consortium (noun) /kən’sɔ:tjəm/ Liên doanh, tập đoàn
a consortium of textile manufacturers
(một tập đoàn của các nhà sản xuất dệt may)
6.Harness (v) /´ha:nis/ Khai thác
the consortium needed to harness the power of radio telescopes all over the planet.
(Các tập đoàn cần phải khai thác sức mạnh của kính thiên văn vô tuyến trên khắp hành tinh.)
7.Murky (adj) /´mə:ki/ Tối tăm, u ám, âm u
murky darkness
(bóng tối dày đặc)
8.Shroud (noun) /ʃraud/ Vật bao phủ, màn che dấu
the whole affair was wrapped in a shroud of mystery
(tất cả vấn đề còn ở trong màn bí mật)
9.Robust (adj) /roʊbʌst/ ngay thẳng
the observations are robust
(các quan sát là ngay thẳng)
10.Predicted (v) /pri’dikt/ Báo trước, nói trước, tiên đoán, dự đoán, dự báo
It’s still not possible to accurately predict the occurrence of earthquakes.
(Vẫn chưa thể dự đoán chính xác sự xuất hiện của động đất.)
Người dịch: Lê Thanh
Nguồn: nationalgeographic.com
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