Услышав эту новость, мама глубоко вздохнула и села на стул.

Услышав is a verbal adverb (also called a gerund or деепричастие in Russian) from the verb услышать (to hear).

In this sentence, it means something like:

• having heard
• after hearing
• when she heard

So Услышав эту новость, мама... literally means Having heard this news, Mom...

A very important point: this form usually shows an additional action connected to the main verb, and in normal Russian it must refer to the same subject as the main clause. Here, the person who heard the news and the person who sighed and sat down is the same person: мама.

Because Услышав эту новость is a verbal adverb phrase, and Russian normally sets this type of phrase off with commas.

So:

• Услышав эту новость, мама глубоко вздохнула...

This is similar to English patterns like:

• Hearing the news, Mom sighed deeply...
• After hearing the news, Mom sighed deeply...

The comma marks that introductory action.

Because it is the direct object of услышав / услышать (to hear), so it goes into the accusative case.

Base forms:

• эта новость = this news / this piece of news

Accusative forms:

• эту новость

Why those endings?

• эта → эту because новость is feminine singular
• новость stays новость in the accusative because it is an inanimate feminine noun ending in -ь

So:

• услышать что? → эту новость

First, мама actually is in the nominative here, because it is the subject of the sentence.

Second, Russian has no articles like a or the. So мама can mean:

• Mom
• mother
• the mother
• sometimes even my mom, depending on context

In this sentence, the most natural translation is probably Mom or Mother, depending on style.

In the past tense, Russian verbs agree with the subject in gender and number.

The subject is мама, which is grammatically feminine singular, so the past-tense verbs take feminine singular forms:

• вздохнул = he sighed
• вздохнула = she sighed

and

• сел = he sat down
• села = she sat down

So the sentence uses:

• мама глубоко вздохнула и села на стул

because the subject is feminine.

Because села means sat down, not was sitting.

This is the difference between:

• сесть / села = to sit down (movement, change of position)
• сидеть / сидела = to be sitting (state)

And the preposition changes with the meaning:

• на стул = onto the chair / to the chair → movement, so accusative
• на стуле = on the chair → location, so prepositional

So:

• села на стул = she sat down on the chair
• сидела на стуле = she was sitting on the chair

Because Russian often uses different cases after prepositions depending on whether you mean movement toward a place or location in a place.

With на:

• на + accusative = motion onto / to
• на + prepositional = location on / at

Here, села describes movement into a seated position, so Russian uses:

• на стул (accusative)

Compare:

• Она села на стул. = She sat down on the chair.
• Она сидела на стуле. = She was sitting on the chair.

Глубоко is an adverb, meaning deeply.

It modifies the verb вздохнула (sighed), not the noun мама. So Russian uses an adverb, just like English:

• глубоко вздохнула = sighed deeply

Compare:

• глубокий = deep (adjective, used with nouns)
• глубоко = deeply (adverb, used with verbs)

Examples:

• глубокий вдох = a deep breath
• глубоко вздохнуть = to sigh deeply / take a deep breath

Yes, both are perfective verbs:

• вздохнула ← вздохнуть
• села ← сесть

Perfective aspect presents the actions as completed, whole events:

• she sighed
• she sat down

That fits this sentence well, because it describes a sequence of completed actions after hearing the news.

If you used imperfective verbs instead, the meaning would change. For example:

• вздыхала = was sighing / used to sigh
• садилась = was sitting down / used to sit down

Those would sound wrong or at least very different in this context.

Yes. In this sentence, Услышав implies that the hearing happened first, and then the main actions followed.

So the sequence is:

1. she heard the news
2. she sighed deeply
3. she sat down on the chair

This is one of the common uses of a perfective verbal adverb: it often shows a completed prior action.

That is why English translations like these work well:

• After hearing this news, Mom sighed deeply and sat down on the chair.
• Having heard this news, Mom sighed deeply and sat down on the chair.

Yes, Russian word order is fairly flexible, though not completely free.

The given order:

• Услышав эту новость, мама глубоко вздохнула и села на стул.

is very natural and neutral. It starts with the background action (after hearing this news) and then gives the main events.

You could also say:

• Мама, услышав эту новость, глубоко вздохнула и села на стул.

This puts мама earlier and inserts the verbal-adverb phrase in the middle. It is still grammatical, but the original version is smoother and more standard in many contexts.

So yes, the order can change, but the original sentence is probably the best basic model for a learner.

Normally, no. In standard Russian, the subject of a verbal adverb should be the same as the subject of the main clause.

So this sentence is correct because:

• мама heard the news
• мама sighed
• мама sat down

All three actions belong to the same person.

English sometimes allows looser constructions, but Russian is stricter here. A mismatched subject can sound unnatural or simply wrong.

Yes, новость is singular:

• новость = news item / piece of news

Russian новость is a countable noun, unlike English news, which is grammatically singular but usually uncountable.

So:

• эту новость literally means this piece of news or this news item

In natural English, people often just say this news, but in Russian it is perfectly normal to use a singular noun here.

Because услышать means to hear in the sense of catching/hearing something successfully, as a completed event.

Compare:

• слушать = to listen
• слышать = to hear, to be able to hear
• услышать = to hear, to catch, to hear something happen or be said

Here the idea is not that Mom was listening, but that she heard the news as a completed event. So услышав is the right choice.

That also matches the rest of the sentence, which describes completed actions.